Abstarct: In this study, two resistorless CMOS voltage reference circuits proposed that both circuit structures are baxsed on PTAT and CTAT in sub-threshold region. In the proposed structures instead of bipolar transistor the CMOS transistors subthreshold region are used for making CTAT voltage. Using CMOS transistors in subthreshold result in decreasing power consumpation. In the first proposed circuit, for PTAT voltage generation two CTAT are used that difference of them makes PTAT voltage. The folded cascode opamp structure (because of its high gain) is used to increase the output voltage accuracy. The proposed circuit generates 0.9V output reference in three switching steps.The circuit dependency to temperature is so very low and it's temperature coefficient is 22 ppm for 0 to 90o. It should be noted that, the proposed circuits are designed baxsed on 0.18 μm CMOS technology and simulated by ADS software.Monte Carlo analysis also shows the average value of the reference voltage (µ) is aboute 0.9V,it's standard deviation is about 0.062 and thus ơ/μ = 6.9%. In the second proposed circuit opamp is removed, PTAT and CTAT voltage are made separately, and a circuit is added at the final step to combine the CTAT and PTAT voltages. All of these changes decrease circuit current consumption significantly to about 345nA. The output voltage of this circuit is about 745mV and it's temperature coefficient is 38.28 ppm for 0 to 90o. Using Monte Carlo analysis, the average value of the reference voltage is about 0.745volts, the output standard deviation is 0.00095 and thus ơ/μ = 0.12%. In both proposed structures, the reference output voltage can be changed by changing the dimension of transistor and also other circuit component parameters.