Purpose: To study the effect of dentin age and adhesive composition on the microtensile dentin bond strengths (μTBS) of five dentin adhe- sives. Materials and Methods: Sixty extracted caries-free human teeth were assigned to the appropriate age group: less than 21 years of age (<21), 21-40 years of age (21-40), and greater than 40 years of age (>40). For each age group, specimens were randomly divided into five dentin adhesives: (1) Adper Easy Bond (EB, 3M ESPE), a one-step self-etch adhesive; (2) Experimental Adper Easy Bond without the Vitrebond Co-polymer (CP) (EBnoCP, 3M ESPE); (3) Adper Single Bond Plus (SB, 3M ESPE), a two-step etch&rinse adhesive; (4) Experimental Adper Single Bond Plus without CP (SBnoCP, 3M ESPE); and (5) Adper Scotch- bond Multi-Purpose (MP, 3M ESPE), a three- step etch&rinse adhesive, as the control group. Specimens were sectioned in X and Y directions and the resulting beams were tested to failure in tension mode at a crosshead speed of 1 mm/min. Statistical analysis was computed using l-test and two-way analysis of variance followed by Fisher least significant difference multiple comparison post hoc test at p < 0.05. Results: The highest mean μTBS values were obtained in the control group (MP) for all age groups. EB resulted in statistically similar mean nTBS compared to EBnoCP for all age groups: p = 0.538 for (<21); p = 0.974 for (21-40); and p = 0.909 for ( >40). SB resulted in statistically higher mean μTBS than SBnoCP for all age groups 0.009 for ( <21); p 0.028 for (21- 40); and p 0.041 for (>40)]. MP, the control group, resulted in statistically lower mean μTBS when applied to the oldest age group (>40) compared to the youngest age group ( <21), at p < 0.04. When means were pooled for the variable 'age group,' SB resulted in significantly higher mean nTBS than SBnoCP at p < 0.009, while EB resulted in statistically similar mean μTBS compared to EBnoCP (p=0.9). MP resulted in statistically higher mean pTBS than all other adhesives-SB (p<0.0001), SBnoCP (p<0.0001), EBnoCP (p<0.022), and EB (p<0.046). Conclusions: The substrate age influenced the bonding ability of the three-step et- ch&rinse adhesive. The presence of a carbox- ylic-based polymer (CP) enhanced the bonding ability of the two-step etch&rinse adhesive.