Correlation between defect structures and light emission from Si-nanocrystal doped SiO2 films has been studied using electron spin resonance ( ESR ) and photoluminescence ( PL ) methods. The ESR analysis revealed the presence of three kinds of ESR centers in the film after annealing at above 900 °C in argon ( Ar ) atmosphere, i.e. Si dangling bond in amorphous Si cluster ( a-center: g=2.006 ), Si dangling bond at Si-nanocrystal/SiO2 interface ( Pb-center: g=2.003 ) and conduction electrons in Si-nanocrystal ( Pce-center: g=1.998 ). Moreover, visible light emission was observed in the annealed sample from the PL measurement. Both the PL intensity and the ESR signal intensity of the Pce-center were increased with an increase of annealing temperature. These results indicate that the Pce-center is strongly associated with the emission center.