Collective and individual emissions from In0.5 Ga0.5 As quantum dots (QDs) in single-defect photonic crystal nanocavities are investigated. When the cavity mode is collectively excited by the QD ensemble, a pair of dipolelike modes with definite linear polarizations is shown. Under low excitations, single-exciton emission lines are resolved. The power dependence of individual QD emissions reveals a nearly tenfold light enhancement for on-resonance QDs. The polarization state of each individual QD is also investigated. It is found that an individual dot could excite either a pure dipole mode or a mixture of both dipole modes. This behavior can be attributed to the random distribution of QDs in the nanocavity.