Abstarct: Mashhad-Chenaran Aquifer with an area of about 2527 square kilometers, as the most sustainable resource supplying the drinking water of Mashhad city, is the most important alluvial aquifer in Khorasan Razavi Province. Unfortunately, despite its importance, comprehensive research to estimate the amount of recharge and determine its origin and elevation has not been conducted. First, groundwater recharge has been estimated using the water table fluctuations method and MRC algorithm in a period of 15 years (Sep. 2001 to Sep. 2016) measured in 31 observation wells. Results suggested that recharge in Mashhad-Chenaran Aquifer follows a certain pattern depending on rainfall fluctuations. Seasonal rainfall starts from the end of October and reaches its maximum in April. The trend of increasing groundwater recharge continues until the end of March, and then, with the beginning of spring, the amount of recharge is significantly reduced. The most important reason for the decrease in recharge rate during this period is the lag time between the beginning of rainfall and its impact on the groundwater. The highest amount of recharge takes place in January, February, and March, and the lowest in August and September. During the 15-year period, the lowest and the highest amounts of recharge were 87.2 MCM (12.4% of rainfall) and 221.7 MCM (29% of rainfall) respectively in 2002-2003 and 2011-2012 water years. During this period, the average annual recharge is about 117.11 MCM (21.21% of rainfall). Recharge less than 5 MCM have the highest frequency and high amounts also has the lowest frequency. Assessing the ratio of recharge to precipitation indicates the correct estimation of recharge by the water level fluctuations method and MRC algorithm. Next, groundwater recharge has been estimated using chloride and isotopic mass balance over a period of three years. During this period, groundwater and rainwater samples were collected and their chloride concentrations and isotopic contents (oxygen-18 and deuterium) were measured in the laboratory. baxsed on the chloride mass balance, the recharge is estimated about 21% (115.79 million cubic meters per year). The mass balance of oxygen-18, suggested that the amount of recharge is about 34.12% (188.39 million cubic meters per year), and baxsed on the mass balance of deuterium, the amount of recharge is estimated to be 24.39% (134.67 million cubic meters per year). The Allison model, which is an experimental model that estimates recharge baxsed on the isotopic content of oxygen-18 and deuterium, has also provided acceptable results. In this model, results show that the amount of recharge for oxygen-18 and deuterium, is estimated to be about 24.75 (136.66 million cubic meters per year) and 26.45% (146.04 million cubic meters per year), respectively. Finally, the results have been controlled and evaluated using the Thornthwaite water balance model and the groundwater balance. baxsed on the results of the Thornthwaite water balance model, the recharge is estimated at 19.24% (106.23 million cubic meters per year) and baxsed on groundwater balance, recharge is estimated at 24.00% (132.52 million cubic meters per year). In this study, the groundwater response to rainfall has been estimated from 31 observation wells by cross-correlation method in a period of 15 years (Sep. 2001 to Sep. 2016). The correlation test results show that after about 2 to 3 months, the effect of rainfall is gradually observed on the groundwater level and the correlation coefficient at the confidence level α = 0.05 and α = 0.1 for 77% and 97% of wells become meaningful respectively. The minimum lag time is 2 months and the maximum is 7 months. In general, the estimated lag time is well matched to the groundwater depth and fully follows the Iso-depth map pattern. The amount of groundwater recharge throughout Mashhad-Chenaran aquifer is mainly controlled by the unsaturated zone properties such as thickness, material, etc. Changes in groundwater depth are the major factor that affects the lag time. With the start of rainfall in late October, groundwater recharge in most wells begins in mid-autumn and continues until late spring. Most of the groundwater recharge takes place in late winter. In summer, rainfall has a very small role in groundwater recharge. In this period, the uncontrolled extraction of water from the aquifer and consequently a sharp and continuous drop in groundwater level plays a major role in water table fluctuations.