The A (1)A(u)(S-1)-X(1)A(g)(S-0) laser-induced fluorescence excitation spectrum of biacetyl has been observed under supersonic jet condition. Three weak bands have been observed at 22 182, 22 169 and 22 278 cm(-1). Having considered the tunneling splitting of G(0)(1) and A(0)(1) bands, the band origin 0(0)(0) is determined at 22 182 cm(-1). The spectrum could be analyzed with three active modes: nu(16)(a(u)) acetyl torsion, nu(15)(a(u)) gearing methyl torsion and nu(21)(b(u)) antigearing methyl torsion. The observed fluorescence spectrum has been completely assigned. The fundamental frequency and anharmonicity constant of acetyl torsion mode are about 87.5 and 5.25 cm(-1), respectively.