Grade 5L API steel is carbon steel that is most often used in the industrial world such as pipe material in the petroleum industry, geothermal industry, and others. However, when compared to other steels such as High Alloy Steel, Stainless Steel, etc. the corrosion resistance is still quite low. One of the corrosion control that can be done is by using an inhibitor. In this study, the inhibitors used were organic inhibitors namely avocado seed extract inhibitors in 3.5% NaCl media and the variables included immersion time and concentration addition. The immersion time is 2 days, 4 days, 6 days, 8 days, 10 days and 12 days, while the concentration used is 0 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm and 5000 ppm. Tests conducted in this study were GC-MS, weight loss, SEM, FTIR, AAS, Polarization and EIS. GCMS results showed the presence of 1,2-benzenedicarboxylic acid compounds; Oleic acid and phenol are compounds found in tannins, thus identifying the presence of tannin in avocado seed extract inhibitors. The weightloss results show that the highest efficiency is found in API 5L Grade B steel with a concentration of 3000 ppm on the 12th day valued at 94.3205%. While the lowest efficiency is at a concentration of 5000 ppm on the second day is worth 47.1747%. SEM results show a thin layer that protects the metal when given an inhibitor and EDS shows that element O has lower levels when given an inhibitor. FTIR results show functional groups such as O-H; C=N; NH3+ and NO2 adsorbed on the steel surface. The AAS results show the levels of dissolved Fe when given a reduced inhibitor. The polarization results show a mixing inhibitor type. And finally EIS testing showed that giving inhibitors showed a decrease in Rs and an increase in Rp when giving inhibitors.