Concrete filled steel square and circular tubular columns are tested. Test is composed of two Series. In Series I, columns are subjected to concentric and eccentric axial force at both ends. In Series II, columns are cantilever columns, and subjected to alternating horizontal load under constant vertical load. As a main experimental parameter, buckling length section depth ratio of a column is selected. Strength and behavior are examined, and design methods for slender composite columns are investigated.