We investigated the incidental encoding in working memory of event serial order in tasks in which the relevant dimension was visual appearance, spatial location, or visual-spatial conjunction. The participants (n = 60) were asked whether two sequences were identical based on the relevant dimension, and to ignore changes in the irrelevant dimension, that is the order of events. Changes in serial order impaired the performance when sequences were identical; this effect was more pronounced in spatial sequences. It is suggested that the order was incidentally encoded with the relevant information to the task in an earlier stage in the information processing, which explains a different pattern of serial order effect according to the relevant dimension. Although encoded, the serial order may not have affected the visual storage in working memory because it might have been kept in a distinct subcomponent rather than the one that stores the visual characteristic. Moreover, the order may have affected spatial storage because the maintenance of this dimension might be related to a rehearsal mechanism based on serial order of sequence. This conclusion qualifies models that admit the architecture of working memory based on the specificity of encoding and functional interaction between subcomponents of storage.