Macrostomum lignano is an emerging flatworm model with remarkable regeneration ability. This ability derives from the unique somatic stem cells - neoblasts. A recent study has shown that a PIWI protein, Macpiwi1, is required for the neoblast maintenance. In order to dissect the roles of PIWI/piRNA pathway in M.lignano, we examined the small RNA and mRNA profiles with and without the depletion of Macpiwi1, Macpiwi2 or biogenesis factor Macvasa. Our study reveals the potential roles of Macpiwi proteins in the hierarchy of piRNA pathway and indicates a separation between transposon silencing and stem cell maintenance mediated by Macpiwi1.