Under laboratory conditions, the African tree rat, Grammomys surdaster surdaster (Thomas & Wroughton, 1908), had four- or five-day oestrous cycles and sterile mating induced a 12- or 13–day pseudopregnancy. Fertile mating resulted in a pregnancy of 24 days and litters usually consisted of two, three or four young. Mating at the post-partum oestrus was rare, but oestrus recurred four or five days later, irrespective of whether or not a litter was being suckled. Conception frequently occurred at this oestrus. Pregnancy length was not influenced by the number of young suckling and delayed implantation was not observed. Puberty usually occurred between 50 and 70 days of age but first conception occurred most frequently between 80 and 100 days of age.