The permittivity was calculated for an optical sensor based on surface plasmon resonance (SPR), in which the receptor-analyte layer is an aqueous mixture of protein microinclusions. These microinclusions together with water form the effective permittivity of the mixture, which depends on the concentration of the inclusions. Also, the effective permittivity of the mixture significantly accounting the dependence of the permittivity of water on temperature and wavelength of radiation. The complex nature of the dielectric properties of a protein molecular inclusion is also accounting. In this case, the imaginary part of the refractive index of a protein molecular inclusion depends on the length of the molecular chain, as well as on the wavelength of radiation. In this study, the effect on the effective dielectric permittivity of the mixture of all the factors listed above (concentration of protein-type inclusions, protein-type chain length, radiation wavelength at normal temperature) was calculated.