In the design of moment connections in steel frames, continuity plates are used to ensure the stability of the panel zone against concentrated loads on the column flange. The criteria for determining the capacity of continuity plates have been developed based on research on the behavior of wide flange sections, and there is limited information on the behavior of box sections under local loads. In this paper, the capacity of continuity plates in box sections under concentrated loads is determined. Initially, a finite element model is created to investigate local instability under concentrated loads and its accuracy is evaluated using available experimental data. Subsequently, the behavior of 56 box column specimens subjected to three types of concentrated loads, including single compression, double compression and single tension was investigated. The governing limit states in column failure were identified as buckling of the continuity plate under compression, yielding of the continuity plate and failure of the loading plate weld under tension. The capacity of the continuity plate in box sections was determined using code provisions and compared with the results of finite element analysis. The investigation revealed that the slenderness of the continuity plate is a significant factor affecting its capacity. Furthermore, the commonly used design criteria for determining the capacity of continuity plates under compressive loads in most columns are non-conservative, resulting in an effective capacity of continuity plates ranging from -28% to 140% of the nominal capacity. However, the provisions presented for determining the capacity of continuity plates under tensile loads show better agreement with numerical analysis results, with the effective capacity of continuity plates under tensile loads ranging from 34% to 137% of the nominal capacity. Modification factors are proposed for determining the capacity of continuity plates under compressive loads in box columns.