Several species of Solanum are used in folk medicine to treat diarrhea. Therefore, the aim of this study was to investigate and compare possible antidiarrheal activity of methanol extracts from roots (Sast-MeOHR) and leaves (Sast-MeOHL) of Solanum asterophorum Mart., Solanaceae, in mice. Sast-MeOHR was shown to significantly and dose-relatedly inhibit the frequency of both solid (ED50 309.6±28.5 mg/kg) and liquid (ED50 152.1±32.5 mg/kg) stools. Conversely, Sast-MeOHL significantly inhibited solid stool frequency only when dosed at 500 and 750 mg/kg (48.7±7.4 and 42.3±9.8%, respectively), but also significantly and dose-relatedly inhibited liquid stools (ED50 268.4±35.2 mg/kg). Thus, Sast-MeOHR was twice as potent as Sast-MeOHL in diarrhea inhibition. Neither extracts (when dosed up to 500 mg/kg) inhibited intestinal transit. However, both extracts significantly and dose-relatedly inhibited intestinal fluids, and Sast-MeOHR (ED50 38.3±10.4 mg/kg) was again twice as potent as Sast-MeOHL (ED50 78.6±6.4 mg/kg). Results suggest that antidiarrheal effects of Sast-MeOHR and Sast-MeOHL involve changes on intestinal secretion. In addition, active metabolites with antidiarrheal activity may be more concentrated in the roots of this species. However further studies are needed to elucidate the action mechanism involved in this activity.