Objective: To evaluate the effectiveness of preanesthesia on ROP laser treatment. Patients: 104 eyes of 52 premature infants with prethreshold and threshold ROP were lasered at neonatal department of National Hospital of Obstetric and Gynecology from 6/2009 - 7/2010. Morphine and midazolam has been used for preanesthesia. Clinical tried study. Results: 100 percent of patients need a single dose of morphine. 17.31 percent of patients need second doses of midazolam. The mean of first dose of these two drugs is 0.064mg + or - 0.013 (0.04 - 0.085mg). The mean of second doses of midazolam is 0.119mg + or - 0.024. The mean time since starting preanesthesia to beginning laser treatment was 20 minutes. The mean time for laser treatment was 52.78 minutes + or - 29.84. The means time for recovering consciousness was 8 hours. 86.54 percent of eyes get good results. With preanesthesia technique laser can be done at neonatal department, avoiding transfer patients to others hospital. Laser can be done on time, no need to postpone, even with infants having systemic diseases. Complication is rare and mild. No infant need converting to general anesthesia, 23.08 percent need oxygen supplementing and mechanic ventilation. Conclusion: Combination of morphine and midazolam can be replaced for general anesthesia in laser treatment of ROP. Good result was 86.54 percent. This method shortens treatment time, required less human resources, equipment and cost. Complication is rare and mild.