Taihang Mountain Area is a high incidence area of esophageal cancer in Northern China Among 124 Rhesus monkeys caught in the area, two cases of esophageal carcinoma were observed in 1990, and their symptoms and pathological morphological structures showed similarity to a well differentiated squamous carcinoma in human. At the same time, the cytological examinations were made on the 89 Rhesus monkeys of different sexes and ages, and the cases for normal (N), light proliferation (LP), high proliferation 1 (HP I) and high proliferation II (HP II) were 27 (30%), 35 (39%), 18 (21%) and 9 (10%), respectively. The proliferation of epithelium of esophagus in Rhesus monkeys changed with increasing age. The average age of the LP was 5.5 years old with the youngest aged 2 and the eldest aged 10; The average age of the HP I was 7.3 with the youngest aged 2.5 and the eldest over 10. The average age of the HP II was 8.1 with the youngest aged 4.5 and the eldest over 10. In all cases, the highest incidence was at the age of 6-10. It peaked at 10 and then decreased with years. The ecological environment (diet, water and soil) for Rhesus monkeys from the Taihang Mountain Area is the same as that for local residents in that area. In the region of a high incidence of human esophageal cancer, the morbidity of proliferation of esophageal epithelium and esophageal cancer was high not only for human but also for animals. And this indicated that the aetiology is closely connected with environment.