Semiconductor alloy nanocrystals CdSxSe1-x of approximately the same size were fabricated by the chemical solution deposition technique. The observed exciton peaks in the UV -Visible spectra show an increased blue shift with the increase in molar ratio (x = 0 → 1). The Effective Mass Approximation (EMA) was applied to determine the size of the nanocrystals using Vegard’s law applied to the bulk parameters. The calculated sizes of alloy nanocrystals are in a good agreement with the directly measured values obtained using high-resolution transmission electron-microscopy (HRTEM). The band gaps vary slightly for the alloyed nanocrystals having the same size but different molar ratio x. The Stock’s shifts determined from the Photoluminence (PL) spectra show no a particular behavior due to the similarity of selenium and sulphur component of the nanocrystals