The unique properties of semiconductor nanowires offer a gateway to improvements in light emitting devices, energy harvesting and conversion. However, in order to better understand the optical properties of these materials, we conducted two-photon excitation photoluminescence (PL) spectroscopy experiments on indium gallium nitride (InGaN) nanowires, which have important applications in light eon diodes (LEDs), and photovoltaics. These nanowires were grown on silicon substrates by molecular beam epitaxy (MBE). We used a house-built two-photon microscope with a tunable femtosecond laser to excite these InGaN nanowires over the infrared excitation spectrum. The PL spectrum peaks at 550 nm. Results show two-photon absorption above the band gap. Also, the PL emission intensity is additionally dependent on the linear polarization angle of the illumination laser. These results indicate anisotropic two-photon excitation in these nanowires, possibly due to the wurtzite crystal structure of InGaN. This discovery will lead to new understanding of electronic and optical properties of InGaN nanowires.