Purpose: This study assessed the influence of new dimethyl sulfoxide (DMSO) containing pretreatments on the aged resin-dentin micro-tensile bond strength (μTBS) of a two-step etch-and rinse adhesive system. Methods: Occlusal enamel of forty-eight sound molar teeth were ground to expose mid-coronal dentin. Prepared specimens were restored with AdperTM Single Bond2 (SB2) adhesive systems. Prior to the adhesive system application, specimens were randomly assigned into three groups according to dentin pretreatment [no treatment (control group), ethanol wet-bonding (EtOH), or 50 vol% DMSO dissolved in ethanol (DMSO/EtOH)]. Resin composite block was build-up for each specimen. Specimens were stored under simulated IPP 20 mmHg, immersed in artificial saliva at 37 oC for either 24h or 6m. Specimens were sectioned into sticks of 1mm2 for μTBS testing using a universal testing machine. Mode of failure was analyzed using a scanning electron microscope. Three extra sticks from each subgroup were prepared and assessed for the amount of silver nitrate penetration (wt%) using energy dispersive analytical x-ray (EDAX). Data were statistically analyzed by Two-way ANOVA of Variance. Results: (DMSO/EtOH) group revealed the highest statistically significant mean bond strength and the least silver nitrate penetration compared to the (control) and (EtOH) groups at 24h and 6m. Adhesive failures was most predominant for control group at 24h, with increased percentage of mixed failure for EtOH and DMSO/EtOH groups at 24h and 6m. Conclusions: DMSO/EtOH dentin pretreatment improved the immediate and delayed resin-dentin bond.