Frugivorous lemurs are thought to be important seed dispersers in Malagasy forests. To evaluate the seed dispersal service offered by dispersers, recent studies have frequently estimated dispersal kernels. To describe dispersal kernels for seeds consumed by lemurs, it is necessary to know the gut passage time (GPT) of seeds. Therefore, the GPT in the common brown lemur (Eulemur fulvus) and the mongoose lemur (Eulemur mongoz) was measured at Tsimbazaza Botanical and Zoological Park in Antananarivo. These species occur sympatrically in northwestern Madagascar. In addition, the size of seeds swallowed and spat out was measured to estimate the upper limit of the size that the lemurs can swallow. The average GPT of seeds in Eulemur fulvus was 229±23 min. The duration of excretion of experimental food was 217±49 min and defecation occurred 16±6 times during the period. Although the average GPT and duration of excretion in Eulemur mongoz were similar to those in E. fulvus, the frequency of defecation in E. mongoz was notably lower, 7±2 times. The GPT of small seeds and large seeds did not differ in the two lemur species. Among primates, these lemurs had a shorter GPT and more frequent defecation. This result reflects the frugivorous digestive strategy and will affect the shape of dispersal kernels. In the measurement of seed size, the width of spat out seeds was greater than the width of seeds swallowed in both species, although the seed length did not differ. Seed width probably decided the upper size limit of seeds that lemurs could swallow. Eulemur fulvus tended to spit out seeds greater than 16.0 mm in width and E. mongoz tended to spit out seeds larger than 7.8 mm in width. Considering the structure of frugivorous communities, this suggests that many large-seeded plants crucially depend on these frugivorous lemurs for seed dispersal in Malagasy forests.