Fine particles (PM2.5) were measured using Airmetrics mini-volume portable samplers during 2nd July and 13th August, 2004 inside and outside nine homes located in generic urban area, roadside area and industrial plant area in Guangzhou city, China. The indoor and outdoor PM2.5 average concentrations (67.7 and 74.5 µg/m3) were about two times higher than the new guideline of WHO, and higher than the levels in other studies (New York, London, Amsterdam, Brisbane, Osaka and Hong Kong, etc). Both indoor and outdoor average PM2.5 concentrations in roadside area (73.5 and 79.4 µg/m3) and in industrial plant area (73.4 and 92.9 µg/m3) were higher than those in generic urban area (56.2 and 51.2 µg/m3). The average I/O ratio in generic urban area, roadside area and industrial plant area were 1.10, 0.93 and 0.79, respectively. The indoor/outdoor correlations of PM2.5 in generic urban area, roadside area and industrial area were from strong (R2 = 0.70, p < 0.001, n = 11) to moderate (R2 = 0.54, p = 0.007, n = 12) and to poor (R2 = 0.17, p = 0.088, n = 12). Strong indoor/outdoor PM2.5 correlation with I/O > 1 in generic urban area indicated excellent ventilation condition at there, good indoor/outdoor PM2.5 correlation with I/O < 1 in roadside area suggested that the indoor PM2.5 were mainly from the outdoor air, and poor indoor/outdoor PM2.5 correlation in industrial plant area was ascribed to seldom ventilation in one home (IS2).