This　paper　presents　the　results　of　an　experimental　investigation　to　determine　the　flexural　fatigue　strength　and　fatigue　life　of　concrete　beams　reinforced　with　monofilament　polyacrylonitrile　fibers　(PAN　fiber　for　short).　The　performance　of　fresh　concrete　and　the　elastic　and　mechanical　properties　of　hardened　concrete　are　compared　by　samples　with　and　without　fibers.　The　toughness　calculated　according　to　both　ASTM　and　JCI　methods　increased　with　the　addition　of　fibers.　The　toughness　indexes　I-5　was　3.8-4.2　times,　I-10　was　5.8-6.8　times　that　of　the　plain　concrete.　The　equivalent　strength　was　0.63-0.87　MPa　for　PAN　fiber　reinforced　concrete.　When　compared　to　plain　concrete,　the　endurance　limit　of　concrete　beams　only　reinforced　with　PAN　fiber　is　increased　by　12　percent.