Purpose / Context - Particulate matter (PM) is one of the main indoor air pollutions, and it can cause a wide range of diseases that lead to a significant reduction of human life. This study aimed at investigating of characteristics of particle concentrations for PM2.5 and size distribution during different activities in residential houses. Methodology / Approach - This study was conducted between December 2013 and January 2014 in 7 houses. The measurements of indoor air were continuously in 24 hours and the instruments were kept in the living room or bed room. Mass concentrations for PM2.5 were measured simultaneously with Dust Trak (TSI/8533). The number size distribution concentrations of particle (10–863 nm) were measured with a portable aerosol mobility spectrometer (PAMS, Kanomax/3300). Results – In each house, the average of PM2.5 concentration was 10-45 μg/m3. The average of I/O ratio of PM2.5 was about 0.5-1.5. Indoor PM2.5 concentration in the living room was increased by using the gas stove, toaster oven in the kitchen and burning candles, incense sticks in the next room. Ultrafine particles with diameters in the range of 30-50 nm were generated by cooking, and the peak particle diameter of I/O ratio was around 50 nm. Key Findings / Implications – The indoor aerosols could be affected by the difference of the ventilation equipment with air filters. The fine and ultrafine particle emissions from candles and incense sticks are generated in indoor. Originality - This study demonstrated the increase of PM2.5 concentrations and ultrafine particle concentrations in the living room due to cooking or other activities with the PM2.5 monitor and PAMS.