The present work is devoted to Raman scattering in (CdS)x(CdSe)1-x nanospheres. Surface phonon modes are observed. Their frequency change, as a function of the alloy content, is analyzed quantitatively. Calculations performed within the framework of the dielectric approaches are found to agree well with the data. Alloying effects and boundary conditions at the sphere- matrix interface are taken into account in these calculations.