A carbodiimide composition having an improved heat resistance which meets conventional requirements for a carbodiimide compound to be compounded in an ester-group-containing resin or a biodegradable plastic, and exhibiting no coloring problems due to yellowing, and having a superior stabilizing effect agains hydrolysis. The carbodiimide composition comprises a carbodiimide compound (A) and an antioxidant (B), having a 5% weight loss temperature not lower than 250.degree. C. as determined by a thermogravimetric (TG) method, wherein an antioxidant (B) is dispersed and present in the composition by admixing during synthesis of a carbodiimide compound (A), a stabilizer against hydrolysis mainly comprising the carbodiimide composition and a thermoplastic resin composition containing the same.