Zn1-xCdxS Nanoparticles with varying Cd concentration were synthesized via co-precipitation technique at 280 K. Despite the analogous size, the nanoparticles with different Cd content exhibit composition-dependent absorption resulting from the distinguished band gap. Due to size effect Zn1-xCdxS nanoparticles, self activated PL band shifted to higher energies compared to the absorption band of bulk counterpart. Origin of the PL emission bands are investigated via fluorescence lifetime measurement. Decay time constant is found in nano second regime and is attributed to the spatial confinement of photo generated electron-hole pairs. © 2010 Bentham Science Publishers Ltd.