Side-stream smoke from cigarettes contains formaldehyde, inhalable particulate matter and other pollutants, which seriously affects human health. The formaldehyde and inhalable particles in sidestream smoke emitted from four common brands of cigarettes in an environmental chamber were monitored by using a hand-held formaldehyde detector and a particulate detector. The concentration of the pollutants was also studied under conditions of closeness, natural ventilation and mechanical ventilation. The results show that the burning rates of four brands of cigarettes range from 2.65 to 3.0 g/h in the enclosed environment chamber and the peak concentrations of formaldehyde emissions range from 1.02 to 1.72 mg/m³. The release process of particulate matter can be divided into release diffusion stage and sedimentation stage. The peak concentrations of PM_2.5 and PM₁₀ is 0.282 and 3.382 mg/m³, respectively. The sedimentation rates of PM_2.5 and PM₁₀ are 0.0180 and 0.0289 mg/m³.h^-1, respectively. It is found that the removal rate of formaldehyde and particulate matter is positively correlated with the ventilation rate. The fitting correlation coefficients of formaldehyde concentration during the rise and fall phases under closed conditions are greater than 0.968 and 0.979, respectively, and the coefficients of PM_2.5 and PM₁₀ are greater than 0.904 and 0.929, respectively.