To evaluate the effect of 2 years of water aging on microtensile bond strength (μTBS) of an etch-and-rinse and a self-etch adhesive system to sound (S) and artificial caries-affected primary dentin (CAD).Occlusal cavities were prepared in 24 primary molars. Half of the specimens were submitted to a pH-cycling model to simulate artificial caries-affected dentin. Teeth were randomly restored either with two-step etch-and-rinse adhesive Adper Single Bond 2 (SB) or two-step self-etch system Adper SE Plus (SE). After 24h of storage, the teeth were sectioned into two halves. One half was sectioned into sticks (0.8mm 2 ) to be tested immediately under μTBS testing. The same procedure was performed in the other half after storage in distilled water for 2 years (2y). Data were analyzed by three-way repeated measures ANOVA and Tukey tests (α=0.05).The μTBS values of both adhesive systems significantly decreased after 2 years aging (SB: S – 38.4%, CAD – 23.9%; SE: S – 17.1%, CAD – 15.7%) (p<0.001). SE showed lower μTBS values compared with SB, regardless of storage period (p<0.001). Higher μTBS were detected in sound dentin, regardless of adhesive (p<0.001).The degradation of the resin-dentin bonds occurred after 2 years of water aging, regardless of the substrate condition or type of adhesive. However, the etch-and-rinse adhesive system is preferable due to the highest μTBS in both periods.