Bonding of brackets is one of the essential factors for successful orthodontic treatment, so bond strength of orthodontic adhesives are very important. The purposes of this research were to compare shear bond strength of various orthodontic adhesives and to evaluate failure sites. One-hundred twenty extracted human first premolars were prepared for bonding and premolar brackets were bonded to prepared enamel surfaces with Super C Ortho, Mono- Lok², Transbond, and Super C Ortho after applying Fluorobond. After bonding of brackets, teeth specimens were divided into 3 groups. In group 1 specimens were stored at humidor 37°C in 1 hour, in group 2 specimens were stored at humidor 37°C in 24 hours, thermocycled 10 times and in group 3 specimens were stored at humidor 37°C in 24 hours, thermocycled 1800 times. Then the universal testing machine Instron 6022, Instron Co., U.S.A. was used to test the shear bond strength of brackets to enamel. After debonding, brackets and enamel surfaces were examined under stereoscopic microscope to determine the failure sites. The results were as follows: 1. Shear bond strength was significantly highest of using Super C Ortho after applying Fluorobond and Super C Ortho In group 1, was highest of using Super C Ortho in group 2, and was highest of using Mono- Lok² in group 3. 2. According to time and temperature change, in using Super C Ortho the group 2 had significantly highest strength and group 3 had lowest strength, in using Mono-Lok² the group 2 and had higher strength than group 1 and in using Super C Ortho after applying Fluorobond shear bond strength decreased constantly. 3. The failure sites were tooth-resin interface in Super C Ortho after applying Fluorobond, Mono Lok² and Transbond and were at almost same ratio bracket base-resin interface and tooth-resin interface in Super C Orth.