A polymer-supported distannane 1 was prepared by treatment of tin halide resin with lithium naphthalenide or sodium naphthalenide in THF. The content of the polymers 1 was determined to be 0.95 to 1.13 mmol/g tin as ditin. The polymer-supported distannane reagent was successfully applied to radical cyclizations of acyclic α-haloesters to yield γ- butyrolactones.