A solid washing agent that is hard even in a high-temperature, high-humidity atmosphere or in a similar environment and that can prevent melting away and stickiness is provided.A composition for a solid washing agent containing an N-long chain acyl acidic amino acid salt as a component of an ingredient wherein the salt for the N-long chain acyl acidic amino acid salt is composed of an alkali metal salt and an ethanolamine salt, the molar ratio of the alkali metal salt to the ethanolamine salt is 10:90 to 75:25, the degree of neutralization is 1.5 to 2.0 eq, and an alkyl-modified silicone represented by formula (I) below is blended as an ingredient, and a solid washing agent formed from the composition.