Purpose: To explore the impact of obesity on in vitro fertilization (IVF) outcomes and comparing the results with regards to age groups. Materials and Methods: This retrospective cohort recruited 780 women that underwent WE Women with polycystic ovarian syndrome (PCOS) were excluded from the study. Women under and above 35 years were categorized into three groups as normal weight, overweight, and obese. The main outcome measures were ovarian response, oocyte maturity, and clinical pregnancy rates. Results: Despite oocyte count and fertilization rate that decreased in both younger and older obese women, this difference was not statistically significant. After age matched-normal weight controls, the clinical pregnancy rates were significantly decreased in older obese women. On the other hand, poor ovarian response observed significantly in young obese women without effect on pregnancy rates. Conclusion: These results suggested that obesity in young and old women has different outcomes and different steps of IVF process may be affected.