Objective To compare the different ovarian stimulation protocols, clomiphene citrate(CC), letrozole, human menopausal gonadotropin(hMG) only or combined with CC or letrozole in women undergoing artificial insemination by donor(AID).Methods In this prospective clinical trial, 671 couples prepared for AID cycles were randomly allocated to 6 groups according to receive different protocols for the first time, natural cycle(group A, n=114), CC(group B, n=101), CC and hMG(group C,n=124), letrozole(group D, n=97), letrozole and hMG(group E, n=123) and hMG only(group F, n=112). Outcomes including total dose of hMG, duration of hMG therapy, dominant follicles number, endometrial thickness, rates of clinical pregnancy,miscarriage, ovarian hyperstimulation syndrome(OHSS), multiple pregnancy and cancelation were compared among the 6 groups.Results The total doses and duration of administered hMG were significantly lower in group C and group E than in group F. Dominant follicle number was significantly less in group A and more in group C than in other groups. Endometrial thickness of group B was significantly lower than that of other groups. Clinical pregnancy rate,multiple pregnancy rate, miscarriage rate, OHSS rate and cancelation rate were not statistically different among the stimulation groups.Conclusion AID cycles in which both CC and letrozole had been administered may require shorter duration and a lower total gonadotropin dose, while the clinical outcomes were similar. Objective To compare the different ovarian stimulation protocols, clomiphene citrate (CC), letrozole, human menopausal gonadotropin (hMG) only or combined with CC or letrozole in women undergoing artificial insemination by donor (AID). Methods In this prospective clinical trial, 671 couples prepared for AID cycles were randomly allocated to 6 groups according to the different protocols for the first time, natural cycle (group A, n = 114), CC (group B, n = 101), CC and hMG 124), letrozole (group D, n = 97), letrozole and hMG (group E, n = 123) and hMG only (group F, n = 112). Outcomes including total dose of hMG, duration of hMG therapy, dominant follicles number, endometrial thickness, rates of clinical pregnancy, miscarriage, ovarian hyperstimulation syndrome (OHSS), multiple pregnancy and canceration were compared among the 6 groups. Results of the total doses and duration of administered hMG were significantly lower in group C and group E than in group F. Dominant follicle number was significa ntly less in group A and more in group C than in other groups. Endometrial thickness of group B was significantly lower than that of other groups. Clinical pregnancy rate, multiple pregnancy rate, miscarriage rate, OHSS rate and cancelation rate were not statistically different among the stimulation groups. Conclusion AID cycles in which both both CC and letrozole had been administered may require shorter duration and a lower total gonadotropin dose, while the clinical outcomes were similar.