In carrying out plastic design for structures, plastic collapse load factor is one of the main parameters for assessing the structural safety. However, in most design codes, the plastic collapse load factor is not clearly defined. Traditionally, the load factor is treated as common to all loads so that they vary proportionally. Although this method has long been accepted in practice, it is in fact contrary to the underlying assumption that the load factor, which is a variable itself, should be applied to design loads which may vary considerably. Therefore, there is suggestion that collapse load factor should be applied separately to loads which may vary greatly throughout the life span of the building. Even for variable loads such as live and wind loads, their degree of variability may differ significantly and it may be appropriate that these loads should be applied with ‘weighted load factor’ in order to have a more realistic collapse evaluation in a plastic design. In this paper, a review of the plastic collapse load requirements in major design codes is carried out, followed by a detailed analysis of the effects of load factor attached to different types of loads in plastic analysis. It is shown that the safety factor resulting from different ways of attaching the load factor to the loads may vary and the degree of variation depends on the load ratios. Finally, recommendations are given for revising the design codes to reflect the degree of variability of the design loads.