The available ASTM recommends grout-filled steel tube anchors (STAs) for the tensile testing of 6.4- to 32-mm-diameter glass fiber-reinforced polymer (GFRP) bars and a 9.5-mm-diameter carbon FRP (CFRP) bar. The available ASTM provides minimum STA dimensions for tensile testing of the FRP bars. However, because of the large variations in the FRP bars, the exact STA dimensions for successfully testing the FRP bars in tension vary significantly and depend on the type and diameter of the FRP bar. In this experimental study, tensile testing of 9- and 15-mm-diameter CFRP bars and a 15.9-mm-diameter GFRP bar was successfully conducted using cement grout-filled STAs. For the 9-mm-diameter CFRP bar, a STA of 31.8-mm outer diameter (OD), 17.6-mm inner diameter (ID), and 460-mm anchorage length (La) was used. For the 15-mm-diameter CFRP bar, a STA of 46.3-mm OD, 27.1-mm ID, and 600 mm La was used. For the 15.9-mm-diameter GFRP bar, a STA of 46.3-mm OD, 27.1-mm ID, and 460-mm La was used. This study investigated the effect of anchorage length of STAs, number of sand coat layers, and grout age on the tensile stress-strain response of the FRP bars. The experimental results showed that increasing the anchorage length of STAs and the number of layers of sand coating improved the frictional resistance between the FRP bars and the surrounding cement grout, which resulted in rupturing of the FRP bars. The experimental results showed that FRP bars with grout-filled STAs tested at 3 days of casting failed by the rupturing of FRP bars, whereas FRP bars with grout filled STA tested at 28 days of casting slipped out from STAs during the tensile test.