The purpose of this study is to verify the effect of lateral position and chest percussion on gas exchange in the decreased level of conscious patients. The Subjects for this study were 21 patients' admitted in ICU of CNUH from Dec 18th, 1989 to Aug 4th, 1990. The Data was analyzed by paired t-test. The results of this study as follows ; 1) In comparison of supine position, good-lung dependent position and good-lung dependent with chest percussion, the difference of PaO was statistically significant(p<0.05). 2) In comparison of supine, good-lung dependent position and good-lung dependent with chest percussion, the difference of A-a Do was statistically significant(p<0.05). In conclusion, the use of good-lung dependent position and chest percussion was effective nursing intervention on decreased level of conscious patients in ICU.