Refractive index dispersion (RID) of fresh tissue is highly related to water content. However, there is no experimental investigation about their relationship for a wide spectral range. In this study, with the aid of a previously proposed lab-made apparatus, the RID of fresh and fully-dehydrated mutton muscle samples were measured over the continuous spectral range from 400 to 750 nm. The mass fractions and volume fractions were also measured. Results showed that the RID of fresh muscle tissue equals to the sum of fully-dehydrated tissue RID and water RID multiplied by their respective volume fractions. The results in this study also experimentally proved that the effective medium theory of refractive index is applicable for tissue analysis. [ABSTRACT FROM PUBLISHER]