Purpose: To investigate the effect of nonnutritive sucking(NNS) on the heart rate, oxygen saturation, and behavioral state of premature infants. Method: From December 15, 2004 to February 15, 2005, 20 premature infants hospitalized in the neonatal intensive care units were assigned to an experimental group (10), or a control group (10). Circular pacifiers for premature infants (Johnson, U.S.A.), which had been packed with $2{ imes}2$ gauzes to create a vacuum, were used for 5 minutes, one hour after feeding for 5 days. Heart rates and oxygen saturation were checked every minute for 10 minutes once a day and behavioral states were monitored through video recording at the same time. Results: Changes in heart rate, oxygen saturation and behavioral state were found to show significant differences between the experimental group and the control group according to the point in time, and interactions were found between the group and the point of time. However, for behavioral state, no significant difference was found between the experimental group and the control group after the NNS was removed. Conclusion: From the results of this study it is possible to conclude that NNS is a positive intervention to bring about increased oxygen saturation and soothed behavioral state for premature infants.