Polyglutamine-binding protein 1(PQBP1)has been identified as one of the disease-causing genes for Mental retardation(MR),but its function and pathological mechanism are still largely unknown.Here we show that PQBP1 play an essential role in neural development through regulating actin dynamics in Drosophila.dPQBP1 mutant flies exhibit severe defects in rhabdomeral morphogenesis as well as in axonal branching of mushroom body neurons.Electron microscopy studies reveal that the defective rhabdomeral morphogenesis in dPQBP1 mutant flies is due to impaired actin nucleation.Immunofluorescence analysis further shows that dPQBP1 co-localizes with actin in the developing rhabdomere in photoreceptors.Further biochemical analysis reveals that dPQBP1 may affect actin nucleation.Our data indicate that dPQBP1 regulates neural development through modulating actin nucleation and offer insights into the mechanism of PQBP1 mutation-caused diseases.