Purpose: This study was carried out to compare between the remineralizing ability of incorporating calcium phosphate nanoparticles (nCaP) into composite and composite without calcium phosphate nanoparticles, using adhesive with and without fluoride on remineralization of caries affected dentin in-vivo. Materials and Methods: The nanoparticles were incorporated into the flowable i-FlowN composite at a mass fraction of 10%. Forty molars in forty patients having class I caries with ICDAS II score 3 were selected. In each selected molar, caries was removed except from the pulpal floor. Thereafter, molars were divided into two groups (n= 20) according to the type composite; resin composite incorporating nCaP and resin composite without nCaP. Each group was further subdivided into two subgroups (n=10) according to the adhesive used; resin composite incorporating nCaP and free fluoride adhesive, resin composite not incorporating nCaP and free fluoride adhesive. All cavities were finally sealed with nanohybride resin composite (Filtek Z350). Assessment of mineral density was performed at base line (C), after one month (C1) and after three months (C3) using digitized radiography. Results: The resin composite incorporating nCaP with adhesive induce the highest remineralization potential during the study intervals followed by resin composite incorporating nCaP free adhesive, then composite free nCaP with fluoride adhesive and lastly composite not incorporating nCaP free fluoride adhesive. Conclusion: nanoparticles are capable of remineralizing the caries affected dentin when incorporated into composite resin and fluoride increase the remineralizing ability.