To provide a new analysis method for analyzing red phosphorus, in a sin composition where metal hydroxide and red phosphorus are used as a fire retardant.

The analysis method of red phosphorus in resin composition, containing metal hydroxide includes a process of separating the red phosphorus from the resin composition by dissolving and removing the resin composing the resin composition with a solvent, and dissolving and removing the metal hydroxide with acid aqueous solution, and a process of detecting the separated red phosphorus with a Raman spectrometer.