Background of the Study: Fiber reinforced composite is a material composed of a polymer resin matrix strengthened by fine thin fibers that are formed as high-strength fibers, easy to bind, biocompatible, have a good aesthetic, colorless and can be attached to the resin structure. The addition of fiber aims to increase the strength of resin composite. Research Objective: This research aims to find out the effects of polyethylene fiber position in the tension zone and the microporosity on the flexural strength of FRC using flowable resin composite. Research Methodology: This is a laboratory experimental research. The materials of the research were polyethylene fiber with a width of 2mm (construct, Kerr, USA), flowable composite resin (Filtek Z350 XT 3M ESPE, USA), silane (Vitique, Germany), and artificial saliva. The sample in this research was FRC rod with size of 25x2x2 mm in one group of fiber position that was at the tension position with total sample size of 4. FRC samples were tested using a Scanning Electron Microscope (SEM) to observe microporosity (mm2) and a Universal Testing Machine to determine the flexural strength. One Way Anova and LSD (P<0,05) test were used to analyze the data. Research Finding: The statistical test of One Way Anova obtains p value = 0,002 where p <0, 05. Thus, there is an effect of polyethylene fiber position in the tension zone and in the microporosity on the FRC flexural strength using flowable resin composite. Sample 4 shows the result of microporosity value of 0, 0077 mm2 with the biggest flexural strength value is 111, 46 Mpa. The mean of the microporosity value of the four samples is 0.7569 mm2 and the mean of the flexural strength is 85.73 MPa. Conclusion: Polyethylene fiber position in the tension zone and in the microporosity affects the FRC flexural strength using flowable resin composite