The body form of holometabolous insects dramatically transforms from larval to adult stages during the pupal developmental stage. In motoneuron "remodelling," larval neuronal cells degenerate and reconnect to new adult muscles. However, the factor that controls location-specific neuronal remodelling has not yet been elucidated. Here, we show that an antioxidant enzyme, Tribolium castaneum superoxide dismutase 6 (TcSOD6), is secreted into the haemolymph and controls the remodelling of adult neuronal cells during metamorphosis. TcSOD6 has a unique domain architecture and is mainly expressed in the pupal developmental stage. The knockdown of TcSOD6 expression in the pupa inhibits axon formation, suggesting a need for SOD activity in neuronal remodelling. Therefore, we conclude that TcSOD6 plays a role in neuronal remodelling during metamorphosis, providing new insights into the evolution of SOD functions.