Gold nanorods with multiple aspect ratios were prepared using seeded growth method. The refractive index sensitivity of nanorods was studied by monitoring the shift of localized surface plasmon resonance peak when the surrounding refractive index was changed. The experiment results show that sensitivity increases almost linearly with aspect ratio. It varies from 216 nm/RIU (aspect ratio 2.5:1) to 352 nm/RIU (aspect ratio 4.2:1) in the monitored wavelength range. Discrete dipole approximation (DDA) is performed to simulate the sensitivity of nanorod with aspect ratio 4.2:1, which is in accordance with the experiment results.