To provide a post body with a rust-proof layer excelling in adhesiveness to the post body, hardness and rust-proofness to effectively prevent the formation of rust, a method for manufacturing the post body, and a rust-proof protective method for the post body effectively preventing the formation of rust.

The post body with the rust-proof layer erected outdoors includes a metal rod-like body (a guardrail pile made of a zinc-plated steel member), and the rust-proof layer formed on the outer peripheral surface of at least a part (a ground side part) of the rod-like body using a photocurable composition for the rust-proof layer. The post body with the rust-proof layer is obtained by carrying out an applying process for applying the photocurable composition for the rust-proof layer to the outer peripheral surface of the rod-like body to form a coating film, and a curing process for irradiating the coating film with light to photocure the coating film to thereby form the rust-proof layer.