Provided is a composition for a refrigeration machine capable of reducing a friction coefficient in friction between sliding members in a refrigeration machine, and a composition kit for a refrigeration machine for providing the composition for a refrigeration machine. A composition for a refrigeration machine of the present disclosure includes a refrigeration machine oil, nanodiamond particles dispersed in the refrigeration machine oil, and a dispersant. The refrigeration machine oil preferably contains a polyvinyl ether, a polyol ester, a polyalkylene glycol, an alkylbenzene, or a mineral oil. The composition kit for a refrigeration machine of the present disclosure includes a refrigeration machine oil (A) containing a base oil and nanodiamond particles dispersed in the base oil, and a refrigerant (B).