Abstract: In order to determine quality of the ambient air in solar greenhouses and its variation pattern, three solar greenhouses, different in operation age, (1, 5 and 10a), were chosen for monitoring of indoor temperature, relative humidity, Cl₂, NH₃, NO, O₃, inhalable particle (PM₁₀) and total suspended particles (TSP), using the in-situ fixed site monitoring method. And on such a basis, quality of the indoor air was evaluated. Results show that the temperature, relative humidity, concentrations of Cl₂, NH₃, NO and O₃ inside the greenhouses were closely related to the outside meteorological conditions, and the concentration of suspended particles increased with the operation age of the greenhouse. Diurnal and monthly variations of Cl₂, NH₃, NO and O₃ did not differ much between greenhouses different in age. The highest concentrations of Cl₂, NH₃ and O₃ occurred at about 14:00, while that of NO did around the times of mat uncovering and covering, NO was negatively correlated with O₃ in concentration (r =﹣0.964). The daily mean concentrations of Cl₂ and the highest concentrations of NH₃ in the greenhouses, regardless of age, all exceeded the national standard, but those of O₃ and NO did not. In terms of concentration of PM₁₀ and TSP, the 10a greenhouse was the highest, and followed by the 5a greenhouse and 1a greenhouse. The concentration of PM₁₀ and TSP in January and February was the highest in a year, and especially in the 10a greenhouse, where PM₁₀ exceeded the national standard for indoor air quality.