We have measured Fourier transform infrared (FTIR) spectra of Cr3+ immersed porous silicon after annealing at different temperatures. After dipping porous silicon into Cr3+ solution, three additional peaks appear at 807, 886, and 940 cm(-1) in the FTIR spectrum. When annealed in nitrogen at different temperatures for various durations, the peak at 807 cm(-1) remains almost unchanged, the height of peak 886 cm(-1) decreases gradually, while the peak at 940 cm(-1) disappears quickly. This decay process occurs much faster at higher annealing temperature. These FTIR features reflect the surface chemistry change after immersed into Cr3+ solution.