Abstarct: In this research, solvent extraction process of lead from sodium hydroxide leaching solution using Tri-butyl phosphate (TBP) diluted in kerosene and its striping by hydrochloric acid were investigated. The influence of important parameters including pH, temperature, extractant concentration, extraction time and organic to aqueous phase ratio were determined on the lead extraction. The results indicated that TBP concentration and phase ratio had the highest effect on lead extraction and an increase in the temperature and organic to aqueous phase ratio is directly related to the increase in lead extraction rate. The highest lead extraction value (93.66%) was obtained at agitation speed of 500 rpm, pH 4, temperature of 40 °C, 1 M TBP concentration, organic to aqueous phase ratio of 5 and extraction time of 20 min. Also, the synergistic effect of organic solvents including D2EHPA and Cyanex 272 with TBP was investigated on the lead extraction rate. The findings demonstrated that the lead extraction rate using TBP is the higher than synergistic extraction system. Thermodynamic parameters including standard enthalpy (∆H), Gibb’s free energy (∆G) and entropy (∆S) for the extraction process by TBP were determined and their amounts were achieved to be 5.88 kJ/mol, -23.47 kJ/mol and 98.5 J/mol.K, respectively, which indicates favorable lead extraction in term of thermodynamics. The McCabe–Thiele diagram was also used to estimate the theoretical stages number of extraction, which the results showed that three stages are required to achieve the maximum extraction of lead in an organic to aqueous phase ratio of 1. Finally, the effect of important factors including hydrochloric acid concentration, stirring speed, stripping time and aqueous to organic phase ratio were evaluated on the lead striping rate. The results showed that among the factors studied, the acid concentration and aqueous to organic phase ratio had the highest effect on lead stripping by HCl and around 68% lead was recovered using 4 M hydrochloric acid at an aqueous to organic phase ratio of 4.