Background: Cocoa seed extract (CSE) is a natural cross-linker or biomodifier, which contains proanthocyanidin that increases the immediate resin-dentin bond strength as well as reduces the dentinal matrix degradation. There are very few studies which shows the long-term effects of the cross-linking agents on radicular dentin. Aim: The aim of this study was to assess and compare the effect of 6.5% cocoa seed extract (CSE) on long-term push out bond strength between fiber post and root dentin cemented by using two different adhesive systems - total etch adhesive system and self-etch adhesive system. Materials and Methods: Sixty extracted permanent maxillary central incisors were decoronated to standardize the root length. Root canal preparation followed by postspace preparation was done. Specimens were then randomly divided into four groups according to the adhesive technique and CSE pretreatment - Group 1: Total-etch adhesive + without 6.5% CSE treatment, Group 2: Total-etch adhesive + with 6.5% CSE treatment for 10 min, Group 3: Self-etch adhesive + without 6.5% CSE treatment, and Group 4: Self-etch adhesive + with 6.5% CSE treatment for 10 min. Fiber posts were cemented with resin cement, and then, specimens were stored in an incubator for 180 days. Specimens were then tested for pushout bond strength using the universal testing machine. Statistical analysis was performed using the one-way ANOVA followed by Tukey's post hoc analysis. Results: CSE-treated groups showed higher bond strength than nontreated group. Group 2 showed significantly higher bond strength among all groups. Conclusion: The pretreatment with Proanthocyanidines containing CSE can be a natural alternative to improve the long-term resin-dentin bond strength.