Observations were made from July 1982 to June 1985 on certain aspects of the population ecology ofRattus rattus wroughtoni Hinton. Altogether 2639 specimens of rats were collected. The male to female ratio was 0·87:1·0. Male rats were significantly heavier and bigger than the females. Pregnant female rats were encountered throughout the year with two peaks, one during early summer (February–March) and the other during monsoon (July–August). The incidence of pregnancy was lowest in May when the day temperature was maximum. The litter size ranged from 1–8. The pre-implantation loss was 0·75 ovum per female.