Abstract: The survey of mouth insertion depths of cigarette filter amongst Chinese smokers was conducted. Two groups of samples were collected. One (1742 butts)was collected randomly from public places in Kunming, Yuxi, Guangzhou, Zhengzhou, Xining, and Beijing, and another (1037 butts)was obtained by returning of the butts from different smokers in Kunming, including civil servants, teachers, students, doctors, and workers, who were selected randomly and given 1600 pieces of cigarettes (800 ventilated and 800 non-ventilated ones each).The mouth insertion depths amongst Chinese smokers was measured by an improved staining method. The tipping paper of the cigarette butt was treated with a 4% (w/w)ethanol solution of ninhydrin and dried naturally under room temperature for 48 hours. The results indicated that 1)the mouth insertion depths of cigarette filters were in a range of 1-17mm and average value 7.3 ±2mm, 2)there was no significant difference among the mouth insertion depths of Chinese smokers at different areas in China, 3)there was no significant difference between ventilated (7.6 ±2.5mm)and non-ventilated cigarettes(7.8 ±2.4mm), and 4) among the ventilated filters measured, only 4% whose ventilation zone had been partially covered and 1% completely covered by smokers' lips.