Statement of Problem: In most shear bond strength (SBS) studies, different cross head speeds have been used.The effect of different speeds on the shear bond strength has been studied in very limited researches.Purpose: The aim of this study was to evaluate the influence of changing cross head speed of testing machine on the shear bond strength and failure mode of orthodontic adhesive (Transbond XT) in bracket bonding.Materials and Method: For this experimental study, 175 human premolars with intact enamels were divided into seven equal groups of 25. After surface preparation, brackets were bonded to teeth using transbond XT adhesive. For debonding process various cross head speeds of 0.5, 1, 2.5, 5, 7.5, 10, 25 mm/min were applied. Shear bond strength and Adhesive Remnant Index (ARI) were recorded for different groups. One way ANOVA and Tukey tests were used for bond strength comparison. Data on shear bond strength evaluations and modes of bond failure were analyzed using Kruskal- wallis and spearman tests.Results: The means of shear bond strength for the applied 0.5, 1, 2.5, 5, 7.5, 10 and 25 mm/min cross- head speeds were 16.39, 14.37, 13.30, 14.12, 13.32, 16.58, and 13.83 respectively. Shear bond strengths in groups receiving 0.5, 10 mm/min cross head speeds, were significantly greater than other groups. No significant differences were obtained between these two speeds, as well as, between 1, 2.5, 5, 7.5, 25 mm/min speeds, but there were significant differences in the shear bond strengths between the two groups with the cross head speeds of 0.5, 10, and 1, 2.5, 5, 7.5, 25 mm/min. Considering the ARI, no differences were found between the groups. Also, there was no relation between ARI and bond strength in groups with different cross head speeds, except in 5mm/min. Conclusion: Cross head speed of Instron is an effective factor on the SBS of the adhesives, but it does not have significant effect on the failure mode of bonding materials.Key words: Shear bond strength, Cross head speed, Transband XT, Bracket bonding.