Purpose: To investigate the effects of root-canal dentin pretreatment with the crosslinker EDC combined with chitosan nanoparticles (Csnp) on the bonding quality of fiber posts in root canals in terms of bond strength, nanoleakage, quantification of collagen degradation, and degree of conversion (DC) of adhesive. Materials and Methods: Forty-eight single-rooted teeth were prepared endodontically and etched using UNI-ETCH (Bisco) as per the adhesive procedure for fiber posts. They were randomly divided into three groups before adhesive (All-Bond 3) application, according to different pretreatments: a. immersed in 2.5% glutaraldehyde for 24 h; b. treated with Csnp solution under ultrasonic agitation for 60 s and immersed in EDC crosslinker for 24 h; c. without treatment (control). Bond strength, nanoleakage, DC within the interface, and collagen fiber degradation were evaluated. Results: The pretreatments had a significant influence on the bonding stability of fiber posts in root canals, but not on the degree of conversion (p = 0.552). Enzymatic degradation significantly influenced bond strength for all groups (p = 0.001), with the greatest effect found in group c. The amount of amino acids released from the adhesive interface differed significantly between groups after hydrolysis and enzymatic degradation (p = 0.000); group c released the highest amount of amino acids. Conclusions: Csnp binding to dentin in combination with EDC reduced degradation of dentinal collagen and improved the stability of the adhesive interface without jeopardizing adhesive polymerization. Keywords: fiber post, root canal, adhesive, bond strength