Endometrial cancer (EC) is one of the gynecologic malignancy cancer with increasing incidence and mortality rates, partly due to aging populations and genetic risks. This study explores the associations between biological age accelerations (BAA) and risk of incident EC and assesses the joint effect of genetic factor and BAA. Based on the UK Biobank cohort, 132,315 women participants were included for primary analysis and 124,119 white participants for genetic risk analysis. Biological age(BA) was calculated using the Klemera-Doubal (KDM) and PhenoAge method based on clinical biomarkers. We calculated two metrics for BAA (including KDM residual and PhenoAge residual) using residual analysis, comparing them against chronological age. The risk of incident EC was evaluated using multivariable Cox proportional-hazards models, adjusting for relevant covariates. Polygenic risk scores (PRS) were computed from known EC-associated SNPs. Both KDM and PhenoAge residual, were significantly associated with increased EC risk. In fully adjusted models, the highest tertile of KDM and PhenoAge residual was significantly associated with incident EC compared with the lowest group, with HRs of 1.278 (P=0.0044) and 1.424 (P<0.0001), repectively. The population-attributable fractions were 7.84% for KDM residual (P=0.0044), 9.78% for PhenoAge residual (P=0.0005), and 8.47% for genetic risk (P=0.0005). Additionally, joint associations of BAA and genetic risk with incident EC was evaluated. Compared with low genetic risk and low BAA, high genetic risk and high BAA was significantly associated with the incidence of EC with HRs of up to 2.172 (95% CI 1.592-2.963) for KDM and 2.226 (95% CI 1.640-3.022) for PhenoAge. Overall, higher levels of PhenoAge residual were consistently associated with an increased risk of incident EC, regardless of genetic risk. BAA and genetics both enhance the risk of incident EC. The effect of the PhenoAge residual is greater than that of the investigated genes, which in turn is greater than that of the KDM residual. These findings highlight the importance of considering both BAA and genetic factors in EC prevention.