Proteins of the ezrin, radixin, and moesin (ERM) family control cell and tissue morphogenesis. We previously reported that moesin, the only ERM in Drosophila, controls mitotic morphogenesis and epithelial integrity. We also found that the Pp1-87B phosphatase dephosphorylates moesin, counteracting its activation by the Ste20-like kinase Slik. To understand how this signaling pathway is itself regulated, we conducted a genome-wide RNAi screen, looking for new regulators of moesin activity. We identified that Slik is a new member of the striatin-interacting phosphatase and kinase complex (STRIPAK). We discovered that the phosphatase activity of STRIPAK reduces Slik phosphorylation to promote its cortical association and proper activation of moesin. Consistent with this finding, inhibition of STRIPAK phosphatase activity causes cell morphology defects in mitosis and impairs epithelial tissue integrity. Our results implicate the Slik–STRIPAK complex in the control of multiple morphogenetic processes.