This in vitro study was performed to compare the microtensile bond strengths (MTBS) of current self-etching adhesives to dentin and to evaluate the effects of artificial aging [(thermocycling (TC) and/or mechanic loading (ML)] on MTBS and on nanoleakage of self-etching adhesives. Two-step (AdheSE Bond, Clearfil Protect Bond, Clearfil SE Bond, Optibond Self-Etch) and one-step (Hybrid Bond, G-bond, Clearfil Tri-S Bond, and Adper Prompt L-Pop) self-etching adhesives were tested. Resin composite build-ups were created, and the specimens were subjected to 104 TC, 105 ML, and 10 4/105 TC/ML. Non-aged specimens served as controls. In the control group, no significant differences were found among the MTBS of the one-step self-etching adhesives and among those of three two-step self-etching adhesives (AdheSE Bond, Clearfil Protect Bond, and Clearfil SE Bond) (p > 0.05). The MTBS of AdheSE Bond and Clearfil Protect Bond were higher than were those of all one-step self-etching adhesives and than those of Optibond Self-Etch. The MTBS of Clearfil SE Bond was higher than were those of two one-step self-etching adhesives (Adper Prompt L-Pop, G-bond) (p < 0.05). Compared with the non-aged controls, TC did not decrease (p > 0.05), but ML and TC/ML significantly decreased the MTBS of the adhesives tested (p < 0.05). Two-step self-etching adhesives tended to fail more cohesively in dentin. Transmission electron microscopy revealed different nanoleakage patterns in the adhesive and hybrid layers of all adhesives examined, and signs of additional silver-filled water channels were more readily detectable after TC/ML. © 2010 Wiley Periodicals, Inc.