The purpose of this paper is an analysis of features of the seismic regime before one of the strongest earthquake Taiwan in the twentieth century (Chi-Chi, 21.09.1999, Mw = 7.6). According to data for 1990-1999 variations of three parameters of the seismic regime were studied retrospectively: total annual number of earthquakes N Ʃ in the range of magnitudes of M L = 2.5-5.5, total annual quantity of released seismic energy ƩE, J and angular coefficient b of graphs of recurrence of earthquakes. There were chosen two obvious sub-periods in course the seismic regime -quiescence in 1990-1996 and activation in 1997-1999. Earthquake of Chi-Chi occurred on a maximum of seismic activity. The prevalence of weak earthquakes during of preparation the Chi-Chi earthquake caused an overestimation of coefficient b graphs of earthquake recurrence (-1.16 on average).