To provide a method for repeatably and quantitatively evaluating degree of insolubility in water of powder containing retinoid and/or carotenoid and having protective colloid as a matrix by the simple operation.

Measurement of the degree of insolubility in water of the powder that fat-soluble materials are held in the protective colloid as the matrix is performed by (a) collecting solid contents from a mixture that the powder and water are mixed and obtaining filtrated liquid by using a filtrating process not to collect the fat-soluble materials extricated from the powder and (b) measuring an optical transmittance of the obtained filtrated liquid.