Concentrations of the airborne particulate matters (PM) in 3 kinds of typical recreation forests in West Mountain of Beijing were monitored day and night in 4 seasons. The observation was made in the Baiwang Mountain. The results showed that: (1) Diurnal variation curves of PM concentrations with 4 kinds of particulate diameters in 3 kinds of typical recreation forests in West Mountain of Beijing all showed nearly “two peaks and two vales” in 4 seasons, and two peaks presented at 5:00-9:00 and 19:00-3:00, and two vales presented at around 15:00 and 5:00 respectively. Peaks and vales time had a minor difference in different seasons. (2) Comparing with other two forests, PM peak time at night in Platycladus orientalis forest occurred later, PM concentration was higher at peaks time, and the duration of the peak was longer. Accordingly, the vale time at night presented also later. Therefore, PM concentration at night in Platycladus orientalis forest with bigger crown density was higher than Cotinus coggygria forest and the mixed forest, especially in summer and autumn. (3) Within a same forest, peaks in day and vales at night of finer particles presented all earlier than that of coarser particles, while vales in day and peaks at night presented later.