In the agricultural field, problems of nematodes are quite important because they cause serious damages upon many kinds of plant. The tests for nematocidal activity of various chemicals were reported^1,2,3,4). But difficulties in assay method for plant parasitic nematodes gave obstacles to the large-scale screening of nematocidal substances. Recently Tarjan²⁾ recommended that Panagrellus sp., a kind of free living nematode, is suitable as assay organism for nematocides because its size (up to about 1.4 mm long) and ease with which it can be cultured. This study was started to find systemic nematocidal antibiotics produced by actinomycetes, using free living nematodes, Rhabditis sp. and Panagrellus redivivus, as assay organisms. Moreover, nematocidal activities of some known antibiotics to these nematodes were also examined.