Photonic band gap of two dimensional photonic crystals fabricated by SiO2/ZrO2 or SiO2/TiO2 with sol-gel process in which the refractive index varied in the range of 1.51 to 1.57 has been investigated in the present paper. The structure studied consists of circular air holes of radius r embedded in matrix, while a is the constant of triangular lattice. Finite difference time domain method (FDTD) with perfectly matched layers (PML) was used to calculate the transmission spectrum by FullWAVE software. The results of simulation clearly demonstrate the existence of photonic band gap of which the position and the width are strongly affected by refractive index. In the other hand, the effects of geometric parameters (air hole radius r and lattice period a) on the photonic band gap have been investigated in this work
