Precise regulation of Notch signaling is essential for normal vertebrate development. Mind bomb (Mib) is a ubiquitin ligase that is required for activation of Notch by Notch's ligand, Delta. Sorting Nexin 5 (SNX5) co-localizes with Mib and Delta complexes and has been shown to directly bind to Mib. We show that microRNA-216a (miR-216a) is expressed in the retina during early development and regulates snx5 to precisely regulate Notch signaling. miR-216a and snx5 have complementary expression patterns. Knocking down miR-216a and/or overexpression of snx5 resulted in increased Notch activation. Conversely, knocking down snx5 and/or miR-216a overexpression caused a decrease in Notch activation. We propose a model in which SNX5, precisely controlled by miR-216a, is a vital partner of Mib in promoting endocytosis of Delta and subsequent activation of Notch signaling.