In recent years, ultrasound has been used as a diagnostic tool to improve fertility in dairy herds. The diameter of the ovarian follicle is highly correlated with the conception rate of the animal, and detecting the presence or absence of cysts in the follicle can play an important role in improving fertility. Therefore, the present study was conducted to evaluate the diameter of the follicle and ovarian luteum (left and right) on the conception rate of dairy cows. For this purpose, 500 dairy cows were ultrasonographed with signs of postpartum estrus. After the initial examination, the cows were divided into 4 groups based on the type of method they were estrused: a) normal b) using PG protocol c) using the Heat Sync protocol d) and using the OV Synch protocol. Also, the studied cows were divided into 4 groups based on the size of the follicle at the time of insemination: a) follicles with a diameter of less than 5 mm b) follicles with a diameter of 5 to 15 mm c) follicles with a diameter of 15 to 20 mm and d) Follicles larger than 20 mm in diameter. Cows with follicles with a diameter of more than 24 mm were considered as follicular cysts. The tested cows were tested for pregnancy on day 30 after artificial insemination and the non-pregnant cows were re-entered into the protocol. Various parameters including follicle size, insemination protocol, corpus luteum size, parity, milk production level, lactation days and insemination month on the conception rate of cows were examined. Left follicle size significantly affected the conception rate (P 0.03) so that the lowest conception rate was related to cows with left follicle size greater than 20 mm (32.4%). By increasing the size of the corpus luteum to more than 10 mm, the conception rate increased (P 0.05). Cows with first parity had a higher conception rate than other cows (60% vs. 43.9%) (P 0.05). The highest rate of conception rate was related to cows with milk production level less than 35 kg (51.4%) (P 0.05). Months of insemination and days in milk were not significantly different conception rates. The percentage of ovarian cysts was significantly affected by parity and month of insemination (P 0.05). In general, the use of ultrasonography to evaluate the condition of the ovaries in dairy cows can increase the efficiency of insemination and consequently prevent financial losses due to pregnancy loss. The results can help in correct reproductive management decisions in dairy cows. Keywords: follicle, corpus luteum, conception rate, ultrasound, dairy cow.