Direct synthesis or CdS nanoclusters within the pore structure or Y zeolite was made. The location of CdS nanoclusters inside Y zeolite hosts was coufirmed by the blue-shifted reflection absorption spectra with respected to that or bulk CdS materials. In this paper, we conducted Positron Aunihilation Lifetime Spectrum (PALS) measurements on a series of CdS/Y zeolite samples and concluded that CdS clusters were not located in supercages but in smaller sodalite cages; as the CdS loading concentration increases to 5 wt%, the discrete CdS cubes begin to form bigger superclusters through interaction. The stability of CdS clusters inside the so- dalite units is due to the coordination of Cd atoms with the framework oxygen atoms of the double six-ring windows. Moreover, PALS reveals some important information of surface states existing on the interfacial layers between CdS clusters and Y zeolite. Direct synthesis or CdS nanoclusters within the pore structure or Y zeolite was made. The location of CdS nanoclusters inside Y zeolite hosts was coufirmed by the blue-shifted reflection absorption spectra with respected to that or bulk CdS materials. In this paper, we conducted Positron Aunihilation Lifetime Spectrum (PALS) measurements on a series of CdS / Y zeolite samples andUTION that CdS clusters were not located in supercages but in smaller sodalite cages; as the CdS loading concentration increases to 5 wt%, the discrete CdS cubes begin to form The stability of CdS clusters inside the so-dalite units is due to the coordination of Cd atoms with the framework oxygen atoms of the double six-ring windows. Moreover, PALS reveals some important information of surface states existing on the interfacial layers between CdS clusters and Y zeolite.