The present invention relates to crystalline polymorphic forms of monosodium N-[8-(2-hydroxybenzoyl)amino] caprylate (SNAC), including two hydrates, a methanol solvate, and an ethanol solvate, of SNAC. More specifically, the present invention provide six polymorphic forms of SNAC (hereafter referred to as Forms I-VI). The present invention also provides an amorphous form of SNAC.