<![CDATA[ABSTRACTBackground: Diametral tensile strength is an important factor in determining the durability of composite resin materials. A reduction in diametral tensile strength increases the risk of fracture and cracking. The incorporation of natural fibers as fiber-reinforced composites (FRC) has been reported to improve the mechanical properties of composite resins. Bemban fiber (Donax canniformis), a plant native to South Kalimantan, contains cellulose and lignin that may enhance the strength of composite resin. Objective: To determine the differences in diametral tensile strength of nanohybrid composite resin reinforced with 10%, 15%, and 20% bemban fiber by volume weight. Method: This true experimental study employed a posttest-only design. Thirty-five samples were divided into five groups: composite resin without fiber reinforcement (negative control), composite resin reinforced with 10%, 15%, and 20% bemban fiber, and composite resin reinforced with polyethylene synthetic fiber (positive control) (n=7 per group). Diametral tensile strength was measured using a Universal Testing Machine. Data were analyzed using normality, homogeneity, One-Way ANOVA, and Bonferroni post hoc tests. Results: Differences in diametral tensile strength were observed among the groups. The highest mean value was found in the 15% bemban fiber group. A significant difference was identified between the 15% bemban fiber group and the group without bemban fiber reinforcement, while differences among the other groups were not statistically significant. Conclusion: There was a difference in the diametral tensile strength of nanohybrid composite resin with the addition of bemban fiber, with the optimal value observed in the 15% bemban fiber group. Keywords: Bemban fiber, Diametral tensile strength, Donax canniformis, fiber reinforced composite, nanohybrid composite resin.]]>
