The aim of the study was to determine an association of TP53 codon 72 (Arg72Pro, G>C transversion, rs1042522) and MDM2 SNP309 (T>G change, rs2279744) polymorphisms in endometrial cancer (EC) of postmenopausal women, regarding grading and staging of EC. In the study, endometrial samples from 202 postmenopausal female patients (the study group, n = 152, was women with EC; the control group, n = 50, cancer-free patients) were taken for the evaluation of two gene polymorphisms: TP53 codon 72 and MDM2 SNP309, respectively. Genotypic analyses were performed using the PCR–RFLP technique. There were significant differences in the frequency of TP53 and MDM2 genotypes in EC patients—increased EC occurrence was observed with the presence of MDM2 G/G and TP53 Arg/Arg genotypes, while allele Pro of TP53 decreased cancer risk. Analysis of combined MDM2/TP53 polymorphisms revealed that T/T-Pro/Arg genotype decreased EC risk, whereas G/G-Arg/Arg genotype increased it. Association of these genetic polymorphisms with histological grading showed increased MDM2 G/G homozygote and TP53 Arg/Arg homozygote frequencies in grading 2 as well as allele G overrepresentation in G1 and G3 EC patients. Finally, with clinical FIGO staging under evaluation, an increase in MDM2 G/G and TP53 Arg/Arg homozygote frequencies in staging I and TP53 Arg/Arg homozygote frequencies in staging II were observed. Co-occurrence of some MDM2 SNP309 and TP53 codon 72 polymorphisms seems to influence EC risk, involving grading and staging of this neoplasm at the same time.