The zebrafish sensory posterior lateral line (pLL) has become an attractive model for studying collective cell migration and cell morphogenesis.Recent studies have indicated that chemokine, Wnt/β-catenin, Fgf and Delta-Notch signaling pathways participate in regulating pLL development.However, it remains unclear whether TGF-β signaling pathway is involved in pLL development.Here we report a critical role of Tgf-β1 in regulating morphogenesis of the pLL primordium (pLLP).The tgfβ1a gene is abundantly expressed in the lateral line primordium.Knockdown or knockout of tgfβ1a leads to a reduction of neuromast number, an increase of interneuromast distance and a reduced number of hair cells.The aberrant morphogenesis in embryos depleted of tgfβ1a correlates with the reduced expression of atoh1a, detalA and n-cadherin/cdh2, which are known important regulators of the pLLP morphogenesis.Knockdown of smad5 affects pLLP development as tgfβ1a depletion and overexpression of casmad5 mRNA encoding a constitutive active Smad5 rescues the defects in embryos depleted of tgfβ1a, indicating that Smad5 mediates tgfβ1a function in pLLP development.Therefore, Tgf-β/Smad5 signaling plays an important role in the zebrafish lateral line formation.