Objective Over the past 20 years, the incidence of endometrial cancer has increased remarkably in Japan. The number of elderly females has also increased within the population of Japan. We examined the impact of advanced age on the demographic and clinicopathological characteristics in Japanese patients with endometrial cancer. Methods Data were collected from 319 surgically treated Japanese females with endometrial cancer from the files of the University Hospital of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu, Japan, between 1990 and 2010. χ2 tests were performed to evaluate the trends in the variables between two decades (A: 116 cases from 1990–2000) and (B: 203 cases in 2001–2010). The histological subtypes were also evaluated based on the immunohistochemical expressions of p53, estrogen receptor, and Ki-67. Results The mean ages ± standard deviation in the decade A group and the decade B group were 57.5 years ± 9.7 years and 61.0 years ± 11.3 years, respectively (P < 0.02). There was an increase in the proportion of patients aged 70 years or older and of high-risk histological tumors including serous carcinoma, clear cell carcinoma, and carcinosarcoma (decade A group and decade B group: 9.5% vs 27.6%, P < 0.001, 10.4% vs 21.6%, P = 0.01, respectively), while the advanced surgical stage (III and IV), obesity (≥25 of body mass index), and nulliparity of the decade A group and decade B group were 23.3% vs 29.1%, P = 0.30, 28.4% vs 33.0%, P = 0.40, and 19.0% vs 21.2%, P = 0.66, respectively. The cancer-specific survival rates in the decade A group and the decade B group were 78.6% and 77.6%, respectively (P = 0.93). Conclusion The increase in number of elderly females in the Japanese population is related to the increase in that of high-risk endometrial cancers. A study is needed to investigate prevention strategies and to improve the treatment of elderly patients with high-risk endometrial cancer.