The influence of the uniformity of geometric fiber arrangement on the fracture behavior was investigated for unidirectional fiber-reinforced composites from both experimental and analytic viewpoints. Two types of mini -composites, composed of 20 carbon fibers and epoxy resin, were prepared using our original method to control the fiber arrangement in experiments: one type had uniform fiber arrangement and the other non-uniform. The tensile tests of these mini-composites showed that the fracture pattern was quite different between the two types of mini-composites, although the difference in the tensile fracture load between them was minimal. A Monte Carlo simulation of the fracture process was carried out using the modified shear lag analysis. The simulation results, showing that the non-uniform fiber arrangement accelerates the crack growth towards the matrix-rich part, accounted for the difference in fracture patterns due to the fiber arrangement.