The rovibrational state dependence of the fluorescence and dissociation yields of acetylene in the (A) over tilde state has been measured. The fluorescence quantum yield varies with a rotational quantum number at the (VK1)-K-3 level, indicating that quenching due to electronic relaxation is present below the dissociation energy. The absolute value of the fluorescence quantum yield, determined for the first time, was only 0.13 at the (VK1)-K-2 J＇ = 2 level located 1778 cm(-1) below the dissociation energy to C2H( (X) over tilde 2 Sigma+) + H(S-2), demonstrating that electronic relaxation is fairly efficient throughout the (A) over tilde state. From the average translational energy release calculated from the Doppler profile of H atoms, it is concluded that dissociation mainly occurs in the (a) over tilde state over the barrier. However, it is also suggested that dissociation from the (VK1)-K-4 and (VK2)-K-4 levels occur via the ground state. The results indicate that internal conversion and intersystem crossing coexist in the decay of the (A) over tilde state acetylene.