The elastic-plastic behavior of reinforced concrete slender columns subjected to biaxially eccentric loads is investigated. A total of 23 column specimens with 12 cm × 12 cm square cross section were tested in three groups ; 7 short columns, whose column length to section depth ratio were 6, and two groups of 8 long columns, whose length to depth ratios were 16 and 26, respectively. Loads were applied monotonically at each column end with equal eccentricities of 0, 0.6, 1.2, 2.4 and 6.0 cm at angles of 0, 22.5 and 45 deg. from an axis of symmetry. The ultimate loads, longitudinal and transverse deformations and the behavior up to failure were examined in detail. The ultimate load carrying capacity of a slender column is reduced by the additional eccentricity due to lateral deflections of the column caused by bending. It is observed that, from data of logitudinal strain, the plane sections remain plane after biaxial bending, and that the maximum compressive strain at crushing of concrete reaches 0.005 when a material failure occurs. Two approximate methods of analysis, proposed by Bresler and Ramamurthy, for calculating the ultimate loads of short columns are examined. Computed results of the ultimate loads are found to agree well with the test results.