We investigated theoretically the polarization characteristics of GaN-based green (525 nm) light-emitting diodes (LEDs) with photonic crystals (PCs) using a three-dimensional finite difference time domain method. The light extraction efficiency depends strongly on the photonic bandgap (PBG) position relative to a frequency (a/lambda) and the depth of air hole for transverse electric (TE) and transverse magnetic (TM) polarizations. The maximum extraction efficiency was achieved when the frequency of a/lambda was matched within PBG region, leading to about 29% (22%) higher than the conventional LED without photonic crystals for TE (TM) polarization. It is found that the polarization of light can be controlled by the a/lambda in PC structure.