Emission quantum yields have been determined for a homopolymer poly(methylphenylsiloxane) and copolymers poly(dimethylsioxane-co-methylphenylsiloxane)s with different methylphenylsiloxane (MePhSiO) contents, together with 3,5-diphenyloctamethytetrasiloxane and 3,5,7-triphenylnonamethylpentasiloxane used as the model compounds, in dilute solvent at different temperatures. Dependence of the monomer and excimer fluorescence quantum yields on the MePhSiO content and temperature has been analyzed. Composition and temperature dependence of the spectral data are well interpreted in terms of the superposition of the photophysical properties originating from each -(Me2SiO)-(MePhSiO)(n)-(Me2SiO)(-) segment in a copolymer chain. It is inferred from the analyses that the mean binding energy of the excimer of the copolymers does not depend significantly on the MePhSiO content.