Abstract: The photosensitive characteristics of five diazido-compounds were studied. By irradiating the toluene solution of these diazido-compounds with high pressure mercury lamp, it is found that within a certain time interval, there are two isosbestic points in the UV spectra of conjugated diazido-compounds. This is time interval of first order kinetics of photolysis. By means of isolation and identification of photodecomposed products of diazido-compounds, the biphotonic mechanism of photolysis is confirmed. Their quantum efficiencies were determined through monochromatic lights which are corresponding to the absorption peaks in the UV spectra.