A method for analyzing a substance, comprising: a step of obtaining a dispersion complex by co-existing fine particles having a dispersion property higher than that of lyophobic fine particles in a dispersion phase of the lyophobic fine particles at a concentration sufficient for covering a periphery of a lyophobic fine particle group; a step of contacting the dispersion complex and a fluid containing an analyte; and a step of analyzing the analyte using an optical measuring means, wherein the lyophobic fine particles exist in the dispersion phase in a group for providing the surface enhancing effect. The method is effective for analysis of a slight amount substance or a low concentration substance.