The East African root rat (Tachyoryctes splendens) is a solitary fossorial rodent occurring in the eastern parts of central Africa. Unlike bathyergid mole-rats, T. splendens occasionally goes aboveground to feed and consequently it is periodically exposed to the natural light–dark cycle. The locomotor activity of T. splendens was assessed under various light regimes. T. splendens entrains its activity to light cycles and displays distinct nocturnal activity with the total percentage of activity during the dark phase at 87.78% ± SD 11.01%. In constant darkness, T. splendens shows free-running rhythms of slightly shorter than 24 h (2340 ± SD 013 h), while still exhibiting most of its activity during subjective night. Upon inversion of the light cycle, time of reentrainment was exceptionally long. Nocturnal activity time (α) was shortened in response to a shorter night length from 1129 to 0746 h; however, when the dark phase was lengthened, α remained roughly similar to that of the 12L:12D photoperiod at 1124 h. A difference in circadian activity is apparent from the laboratory and field findings, thus in a natural situation, other environmental factors may influence activity patterns.