The aim of the study is to know the effectiveness of clomiphene citrate and letrozole for ovulationrelated to endometrial thickness and number of dominant follicle. Study design was cross sectional basedon medical records of women who underwent ovulation induction from January 2011-May 2015. A numberof 143 anovulation women were divided into clomiphene citrate 50mg, clomiphene citrate 100 mg, letrozole2.5mg and letrozole 5mg. Each group received the agent daily on 3rd-7th day of menstrual cycle. On 12thday of menstrual cycle, the transvaginal ultrasound was performed to measure endometrial thickness anddominant follicle number. From all subjects, 45 subjects (31.5%) were in 50mg clomiphene citrate groups, 29subjects (20.3%) in 100mg clomiphene citrate group, 23 subjects (16.1%) in 2,5mg letrozole group, and 46subjects (32.2%) in 5mg letrozole group. Subjects who received letrozole had thicker endometrium comparedto clomiphene citrate (p<0.05). Different doses were not associated with endometrial thickness betweensubjects who received either letrozole or clomiphene citrate. In addition, subjects receiving letrozole hadhigher proportion of having trilaminar endometrium morphology. We did not observe the difference in totalnumber of dominant follicle between groups. It is concluded that letrozole is more effective than clomiphenecitrate in terms of endometrial thickness but not for number of dominant follicles.