Monitoring of PM₁₀ and PM_2.5 particularly in school microenvironments is extremely important due to their impact on the global burden of disease. PM₁₀ and PM_2.5 levels were monitored inside and outside the classrooms of twelve naturally ventilated schools located in Gaza strip, Palestine. The measurements were carried out using hand held particulate matter instrument during fall, winter and spring seasons from October 2011 to May 2012. The average concentration of indoor PM₁₀ was 349.49 (±196.57) μg m⁻³ and for PM_2.5 was 103.96 (±84.96) μg m⁻³. The indoor/outdoor ratios for PM₁₀ and PM_2.5 were found to be much greater than 1.00 for all case study schools due to resuspension of deposited particles from the floors. Furthermore, strong correlations were found between indoor–outdoor PM₁₀ and PM_2.5. The variations of PM₁₀ and PM_2.5 concentrations were significant for the three seasons. During winter, the mean indoor PM₁₀ was 1.30 and 2.50 times higher than fall and spring concentrations respectively. Meanwhile, PM_2.5 concentration in winter was 3.00 times higher than fall and spring concentrations. In relation to spatial variation, the concentration of PM₁₀ in the lower storey level was significantly higher than the classrooms located in the higher storey level.