Abstract This study examined the effect of the concrete unit weight on the seismic performance of reinforced concrete columns. Three types of columns all-lightweight aggregate concrete, sand-lightweight aggregate concrete, and normal-weight concrete (NWC) were prepared with different amounts of transverse reinforcement and magnitudes of the applied axial load level. Nine columns were tested to failure under constant axial load and cyclic lateral loads. The axial force–moment interactions of column specimens were compared with the predictions obtained by ACI 318–19 procedure using the equivalent stress block and section lamina approach considering the actual stress–strain relationships of various concrete types. The curvature ductility ratios determined from the columns were compared with the ductility-based design procedure specified in EC 8. Test results showed that the moment capacity of lightweight aggregate concrete (LWAC) columns is lower than that of NWC columns, yielding that the safety of ACI 318–19 procedure slightly decreases for columns with a lower concrete unit weight and under lower applied axial load level. The ductility of columns also decreased with a decrease in concrete unit weight, revealing lower values of displacement ductility ratio and equivalent damping coefficient for LWAC columns than NWC columns. Thus, LWAC columns require more transverse reinforcement to achieve a similar seismic ductility to NWC columns under the same design conditions.