Radiation characteristics of various microstrip MIC passive elements are investigated in detail on the basis of accurate numerical analysis. For this purpose, the FD-TD method combined with the radiation mode theory is used. Summarized results are presented mainly from the viewpoint of making clear how radiation characteristics differ depending upon typical features of element structures and operating frequencies. Particularly important features of this paper are that not only radiation into the space region but also that in the substrate region is studied in detail for the first time. Suggestive remarks are given on positioning of active devices in MIC for avoiding interference from nearby elements.