An antagonistic rhizoplane bacterium (Serratia Marcescens) and a chitin-degrading microbe (Streptomyces anulatus) were used for establishing a binary microbe system for biological control of Fusarium wilt disease of tomato. For effectively tracing root-colonization, the rhizoplane bacterium was genetically marked with the lux genes and the tetracycline resistance gene through bacterial conjugation. Successful colonization by the bacterium on roots from bacterized seeds was visualized by bioluminescence of the transconjugant into which the lux gene operon had been integrated. Antifungal activity of the transconjugant was stable and effectire even when the bacterium was colonized on tomato roots. Multiplication of the transconjugant in soil was supported by the chitin-degrading microbe which had been previously added in chitin-supplemented soil. The chitin-degrading microbe produced extracellular endochitinases and hydrolyzed chitin which was added to soil. Chitohydrolytic products supported the multiplication and root-colonization of the rhizoplane bacterium in soil. The binary microbe system comprising of chitin-degrading microbe and gene-marked transconjugant was effective in controlling of tomato wilt disease caused by Fusarium oxysporum f. sp. lycopersici.