A study in relative ratio of air sampleing by open-face and closed-face cassettes of 37 millimeters at angle position Degree 0 Degree 45 and Degree 90 in dust tunnel with the air velocity of 0.8, 1.2 and 1.6 m/sec. Wood charcoal dust size 5.2, 10.5, 38, 45 and 53 ...m, were obtained respectively for study and the result is stated as follows:- Air sampling relative ratios by open-face and closed-face cassettes were 0.93 adn 0.75 respectively. A comparison by statistical analysis showed that open-face cassettes relative ratio is higher than the closed-face cassettes with 95% comfidence. The cassettes at angle of Degree 0 , Degree 45 and Degree90 resulted the air sampling relative ratio of 1.25, 0.97 and 0.3 respectively. Besed on statistical analysis, the air sampling relative ratio of Degree 0 angle-cassette is significantly more than the relative ratio of boht cassettes with angle of Degree 45 and Degree 90 with 95% confidence. At the fixed air velocity of 0.8, 1.2 and 1.6 m/sec, the air sampling relative ratio will be 0.61, 0.73 and 1.18 respectively. According to statistical analysis, the air sampling relative ratio at the high velocity of 1.6 m/sec is significantly more than the relative ratio at air velocity of 0.8 and 1.2 m/sec. with 95% confidence.