Research has been carried out on the effect of the concentration of Kepok banana peel extract as an inhibitor on API 5L carbon steel in 3% NaCl corrosive medium. API 5L carbon steel immersion was carried out for 7 hours with two variations of immersion temperature, namely 40 and 80 oC and five variations in the concentration of corrosion inhibitors, namely 0%, 2%, 4%, 6%, 8%. Corrosion rate testing was carried out using the weight loss method. The results showed that the largest corrosion rates at immersion temperatures of 40 and 80 oC were at 0% inhibitor concentrations, namely 60.91 mm / y and 86.91 mm / y. Meanwhile, the lowest corrosion rate was at the inhibitor concentration of 8% at immersion temperatures of 40 and 80 oC, namely 32.51 mm / y and 63.92 mm / y. The greatest effectiveness of corrosion inhibitors occurred at a concentration of 8% at immersion temperatures of 40 and 80 oC of 56.63%, and 26.44%. The results of the X-Ray Diffraction (XRD) characterization showed that the phase formed was pure Fe. Scanning Electron Microscopy (SEM) characterization showed uneven clusters and smaller size, holes and cracks were also less in 8% inhibitor at immersion temperature of 40 and 80 oC compared to inhibitor 0% at immersion temperature 40 and 80 oC.