Background: partial caries removal has received an increasing interest of dental clinicians and researchers with growing evidence of potential clinical effectiveness and long-term reliability. Objective: This is a prospective clinical study into the biological reliability of partial caries excavation in class II resin composite restorations. Materials and Methods: 40 patients with one deep class II lesion have been recruited for the study (n=20). Class II cavities were prepared to produce sound enamel walls and hard superficial dentin at cavity peripheries. Recruited subjects were classified into two groups according to the clinical end point of caries excavation. In group S, a layer of soft caries is left behind while in group L, caries was excavated till leathery/firm dentin. A universal adhesive system was used employing the selective enamel etching strategy. A nanohybrid resin composite Neo Spectra ST was used to fill the cavities. Restored teeth were assessed at one week, three months, 6 months, and 12 months respectively for pulp vitality and post operative hypersensitivity. Results: None of the restored teeth showed signs of irreversible pulpitis or apical periodontitis after 24 months of restoration. Although S showed greater incidence of hypersensitivity at 2 weeks and three months intervals, there was insignificant difference between the test groups at 6 months and 12 months respectively. Conclusion: Partial caries removal appears to be a clinically effective procedure that preserves pulp vitality in deep class II restorations.