Taking Jinyun Mountain in Chongqing, southwestern China as an example, we observed PM2.5 in four kinds of typical forest stands (Phyllostachys heterocycla forest, broadleaved forest, coniferous forest and Pleioblastus amarus forest) in summer and autumn seasons, and detected particles of different sizes (TSP, PM10, PM2.5 and PM1) at different time of the day in typical weather of different seasons to explore how typical weather conditions influence the concentrations of atmospheric particles of varying diameters in these forests in southwestern China. The results showed that: PM2.5 mass concentrations were higher in autumn than in summer. There was no difference in the concentrations of different particles in the four kinds of forest in summer, while in autumn, the concentrations of particles in Pleioblastus amarus forest were significantly higher than those in other three kinds of forest. The diurnal variation in PM2.5 followed the order of morning > noon > night. PM2.5 concentration declined irregularly in summer, while it was just the opposite in autumn. Under four typical weather conditions, the particle concentration was the lowest after rain, especially for fine particles, showing that rainfall played a positive role in reducing particulate matters. Concentrations of particulate matters were significantly higher in summer drought weather than in the other three typical weather conditions. Different weather conditions had significant influence on the concentrations of particulate matters in Phyllostachys heterocycla forest, coniferous forest and Pleioblastus amarus forest. The sunny weather after rain and continuous sunny weather had no significant influence on the concentrations of particulates in the broadleaved forest.