This study evaluated the degree of conversion (DC) and adhesion of methacrylate-based resin cements to glass fiber posts at different regions of intraradicular dentin. Single-rooted teeth (N=24, n=12 per group) were cut at the cement-enamel junction (CEJ), endodontically treated and post space (depth=8 mm) was prepared. Teeth were randomly divided into two groups according to the resin cements: (a) Group ML: methacrylate-based cement with phosphonic acid acrylate (Multilink Automix, Ivoclar Vivadent); (b) Group RXU: methacrylate-based cement with phosphoric acid acrylate (RelyX Unicem 2 Automix, 3 M ESPE). Fiber-reinforced composite root posts (RelyX Fiber Post, 3M ESPE) were cemented according to the manufacturers' instructions of the resin cements. Root slices of 2-mm thickness (n=3 per tooth) were cut below the CEJ 1, 3, and 5 mm apically. The DC of each section was analyzed with micro-Raman spectrometer and push-out test was performed in the Universal Testing Machine (0.5mm/min). After debonding, all specimens were analyzed using optical microscope to categorize the failure modes. While data (MPa) were statistically evaluated using Kruskal Wallis, Mann-Whitney U tests for DC data 3-way ANOVA and Tukey's tests were used (=0.05). Regardless of the resin cement type, the mean push-out bond strength results (MPa), were significantly higher for the coronal slices (ML: 9.1 +/- 2.7; RXU: 7.3 +/- 4.1) than those of the most apical ones (ML: 7 +/- 4.9; RXU: 2.89 +/- 1.5) (p=0.002). Resin cement type and (p<0.001) root level (p=0.002) significantly affected the DC values, while the interaction terms were not significant (p=0.606). Overall, DC was significantly higher for ML (67 +/- 8.2%) than RXU (26 +/- 8.8%) (p<0.001). Adhesive failures at the cement-dentin interface were more commonly experienced in RXU than in ML, whereas ML presented more incidences of adhesive failures at the cement-post interface. Considering the push-out bond strength, DC and failure types, methacrylate-based cement with phosphonic acid acrylate should be preferred to those containing phosphoric acid to adhere glass fiber posts in the root canal.