Epilayers of erbium-doped GaN (GaN:Er) were synthesized by metal-organic chemical vapor deposition, and the optical excitation cross section (σexc) of Er ions in this host material were determined. Photoluminescence (PL) measurements were made using laser diodes at excitation wavelengths of 375 and 405 nm, and the integrated emission intensity at 1.54 μm was measured as a function of excitation photon flux. Together with time-resolved PL measurements, values of σexc of Er ions in GaN:Er were obtained. For excitation at 375 nm, the observed excitation cross section was found to be 4.6 × 10-17 cm-2, which is approximately three orders of magnitude larger than that using resonant excitation. Based on the present and previous works, the optical excitation cross section σexc of Er ions in GaN:Er as a function the excitation wavelength has been obtained. The large values of σexc with near-band-edge excitation makes GaN:Er attractive for realization of chip-scale photonic devices for optical communications.