Backgrounds: Polycystic Ovary Syndrome (PCOS) is one of the most common causes of female infertility due to ovulation disorders. Clomiphene citrate (CC) is a first choice to restore ovulation but it has some side effects by estrogen receptor down-regulation. Aromatase inhibitor (AI) is a newer class of drugs which increases the production of endogenous FSH to stimulate ovulation. Subjects and methods: randomized control trial to compare 64 cases of infertile women with PCOS examined at the Hue University Hospital, alternately used AI (group I) or CC (group II) for ovulation induction from day 2 cycle. Follow-up follicle growth, endometrium and ovulation via ultrasound. Evaluation were done on 10th day cycle, day of hCG trigger and after administration of hCG. Results: Total of 64 PCOS cases distributed into 2 groups using alternatively AI and CC had similar characteristics with average age of 28.8 ± 4.6, the majority were primary infertility (84.4%), infertility duration was 2.6 ± 2.4 years, 85.9% had oligomenorrhrea or amenorrhea, normal body mass index accounts for 60.9% and 21.9% was lean. Evaluation of both groups on day 10 revealed no differences in the dominant follicle and endometrial thickness. Number of days until the follicle mature appears to be shorter in AI group (15.1 ± 2.9) compared to the CC group (16.5 ± 2.8) with statistical significance. The number of mature follicles in 2 groups were not different at a rate of 81.3% (AI) and 84.4% (CC) but a higher proportion of single mature follicle in the AI group (71.9%) compared with the CC group (65.7%) and There is no case with 3-4 mature follicles in the AI group. The rate of thin endometrium (<8 mm) in the AI group (25%) was lower than the CC group (53.1%) with statistically significance and higher ovulation rate (68.8%) compared with the CC group (56.3%) but have not found statistically significant. Conclusion: Two drugs AI and CC potentially induce follicle development and ovulation similarly, but AI has the potential to be more effective than CC on factors such as the shorter stimulation duration, increasing rate of single follicle, limiting multiple pregnancies, improve endometrial thickness and higher ovulation rate. More researches are needed with a larger sample size to clarify the statistical significance of differences.