Abstract: It is shown from the data of SARS in Beijing that, since late April, the relative rate of increase in the number of cases decreases continually as the cumulative number of patients increases. By assuming that this is a linear decrease, it can be found that the number of patients as a function of time is a reverse Fermi－Dirac distribution. Based on the data to date, it can be expected that the SARS epidemic in Beijing will be controlled by the middle of June, and the total number of cases will finally be around three thousand.