The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range 190-660 nm. The dissociative excitation and dissociative ionisation associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A-X), CH(B-X), CH + (B-A), and C2).Besides the discrete transitions we have detected the continuum emission radiation of ethynyl radical C2H(A-X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholds of the particular dissociative channels.