A grating-coupled surface plasmon resonance sensor based on bilayer aluminum nanowire arrays is fabricated by laser interference lithography. The device presents impressive reflective sharp peaks by lateral surface plasmon resonances even for aluminum thicknesses of merely several nanometers. Distinct reflective peaks and dramatic color shifts under different analytes are observed within a wide range of incident angle, metal thickness, and refractive index. The sensitivity of 307 nm per refractive index unit is experimentally obtained. The reflective-peak-type surface plasmon resonance sensors are suitable for practical applications because of easy fabrication, low cost, wide range, and high signal visibility.