Cathodic protection is being applied to buried steel pipelines and polarized potential of pipelines is kept less noble than the protection potential criterion, -0.85 V vs. Cu/CuSO₄. However, instantaneous anodic current has been infrequently observed in some fields even though polarized potential of pipelines is kept less noble than the protection potential criterion. In this study, the influence of instantaneous anodic current on corrosion protection of buried steel pipelines under cathodic protection was evaluated and the oxidation reaction causing anodic current was investigated to some extent. As a result, it was found that most of the anodic current was not attributed to corrosion reaction and the maximum value of corrosion rate of steel was as little as 1.8 μm/year. Therefore, it was considered that there was no matter on buried steel pipelines even though the instantaneous anodic current occurred under the protection potential criterion. It was estimated that some part of the anodic current was attributed to the oxidation reactions of components in soil and of rust on the steel surface.