The spatial variation of the optical properties of hillocks in Al 0.11Ga0.89N films has been studied by using microphotoluminescence (μ-PL) microscopy. The μ-PL spectrum revealed a strong emission (IH) at 351 nm from the hillock, besides the near-band-edge emission (Inbe) at 341 nm. Moreover, the IH intensity increases significantly and its full width at half maximum decreases from ∼76 to ∼53 meV by probing across the hillock center. These indicated that the hillock structure is a strong emission center. The temperature-dependent μ-PL measurements showed that the IH also has the S-shape behavior with a transition temperature of ∼120 K which is lower than that of Inbe. The redshift of IH is also smaller than Inbe. Both indicated that the Al composition in hillocks is lower than the surrounding area.