Clustering of acoustic emission (AE) in space and time was found in a laboratory experiment. To investigate the stochastic process of AE occurrence, event times of AE were measured during steady creep phases under different stress levels. Oshima granite was continuously subjected to constant uniaxial stress of different intensity. The occurrence time of AE event was analyzed as a combination of a Poisson process and a self-exciting part; in the latter, events are excited by preceding events. The self-exciting character was more enhanced under higher crack density, in accordance with a stronger concentration in hypocenter distribution at higher stress. ¿ American Geophysical Union 1990