Introduction: Infertility is a common issue among married couples in Bangladesh. Infertility is often caused by a combination of multiple factors, and that individual cases of infertility can be complex and difficult to diagnose. Objective: To assess the determinants of infertility among the infertile couples both male and female. Materials and Methods: This prospective observational study was conducted in the Infertility unit, Department of Obstetrics and Gynaecology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, during the period from 01.07.2018 to 30.31.12.2021. Five hundred infertile couples were recruited from the out-patient department of infertility unit who came to take treatment for their infertility problem. Results: Mean (± SD) age of the female patients was 27.1 ± 5.2 years ranged between 18-44 years. Mean (± SD) age of the husband of patients was 34.0 ± 5.9 years ranged between 22-55 years. Primary infertility was seen in 59.8% study subjects and secondary infertility was seen in 40.2% study subjects. In our study, most of the women (94%) had below normal (<3 U/L) serum FSH. Most of the women (96%) had below normal (< 2U/L) serum LH. Serum TSH was normal (0.2 – 4.5 mU/L) in 51.0% patients. Majority of the women (60.8%) had above normal (>21 pml/L) serum FT4 level. Most of the women 72.2% had normal serum prolactin level. In male patients, Testosterone level was above normal (>30 nmol/L) in majority of the patients (73.4%). In Hysterosalpigography (HSG), 0.40% had abnormal uterine cavity, 4.2% had septed uterus, 15.2% had bicornuate uterus, 1.0% had unicornuate uterus and 1.6% had endometrial polyp. Hysteroscopy found abnormal uterus in 1.2% of patients, abnormal uterine cavity in 11.4%, abnormal endometrial flakes in 12.4%, abnormal right ostium in 13.0% and abnormal left ostium in 12.6%. Intrauterine adhesion, polyp and submucus fibroid were found in 35.2%, 2.8% and 17.6% respectively. Laparoscopy found abnormal uterus in 3% patients, abnormal right fallopian tube in 33.2%, abnormal left fallopian tube in 34.2%. Also, abnormal right fallopian tube in 37.0% and abnormal left fallopian tube in 37.6%. Pouch of Douglas free was found in 63%. During dye test in laparoscopy, 57.6% patients were found positive. In quality, semen type was found poor (<4%) in majority (61%) of the husbands. Regarding semen count, above normal (>20 million/ml) level was found in majority of the patients (80.8%). Regarding semen quality, majority (96%) had oligospermia (<15 million/ml). In case of rapid linear (RL), normal (50-60%) level was seen in majority of the patients (81.6%). In case of slow linear (SL), below normal (<15%) was seen in majority (64.8%) of the patients. Regarding non-propagative (NP), normal (0-10%) level was seen in most of the (87.8%) patients. In case of morphology of sperms, above normal (>50 million/ml) level was seen in most of the patients (80.6%). Conclusion: This study shows that a significant percentage of both male and female are suffering from infertility. The major causes of male infertility are partly hormonal, structural abnormalities of male genitalia, infection of genital tract, and partly psychological. Causes of female infertility are mostly hormonal, structural abnormalities of the uterus, fallopian tubes, infection of the genital tract and partly psychological.