OBJECTIVE To evaluate the penetration of two different adhesive resin systems into cavitated and non-cavitated artificial carious lesions and the behavior of treated carious lesions under further acid attack. METHODS Artificial caries-like lesions were created on the proximal surface of 100 human primary molars by a demineralizing gel. The teeth were assigned to three groups according to the adhesive resin used. Group 1 (G1) was for Single Bond adhesive resin, Group 2 (G2) for Xeno V adhesive resin, and Group 3 (G3) was without any adhesive application. Each group was randomly and equally subdivided into subgroups a and b. In subgroup a, the teeth were kept with intact artificial caries-like lesion surfaces while in the subgroup b, a minute cavity was made at the center of artificial caries-like lesions using a sharp explorer. Each tooth was sectioned occluso-cervically into two halves through the center of the lesion; the sectioned surface was polished and examined under a reflected light microscope for estimating the depth of the carious lesion or penetration of the adhesive resin. All tooth halves were coated at the sectioned surface with two layers of acid resistant nail varnish and returned again to the demineralizing solution to assess the progression or arrest of the carious lesion after the second acid attack. RESULTS The penetration depth of adhesive resins did not differ significantly between subgroups (P>0.05). After the second acid attack, the infiltrated carious lesions showed no lesion progression while the non-infiltrated lesions showed advanced caries progression.