Lightweight polymer concrete with steel fiber can be used for thin panel, high building and large span structures due to its may advantages such as its durability, low weight, control of crack propagation, high strength and toughness. This study experimented about steel fiber reinforcement of lightweight polymer concrete using synthetic lightweight aggregate. The test result shows that the maximum strain and elastic modulus are in the range of 0.012 -0.014 and 50.2 x 10³~51.0 X 10³ kgf/cm², respectively. The flexural load-deflection curves after maximum load are shown in smoothly with increase of steel fiber content