The activities of enzymes responsible for disease resistance in Coleus forskohlii, pre-inoculation with an arbuscular mycorrhizal fungus, Glomus fasciculatum, and/or infection with a pathogenic strain of Fusarium oxysporum, and the biological control effect of G. fasciculatum on fusarial wilt in Coleus forskohlii were investigated. The experiment was carried out with four treatments, viz. plants pre-inoculated with G. fasciculatum, plants pre-inoculated with G. fasciculatum followed by infection with F. oxysporum, plants infected with F. oxysporum, and plants without any of the two microorganisms. Mycorrhization (%) was reduced in pathogen-challenged plants. In G. fasciculatum- and F. oxysporum- treated plants, an increase in phenolic content was observed on the 20th day while the maximum increase in phenylalanine ammonia-lyase activity was observed on the 15th day after challenge inoculation with F. oxysporum compared with that of other treatments. In G. fasciculatum- and F. oxysporum-treated plants, an increase in peroxidase and polyphenol oxidase activity was observed on the 15th day after pathogen challenge compared with that of other treatments. The observation revealed that the arbuscular mycorrhizal fungus Glomus fasciculatum systemically induced resistance against wilt disease of Coleus forskohlii via production of phenolics, the defence enzymes phenylalanine ammonia-lyase and polyphenol oxidase, and pathogenesis-related proteins, and peroxidase in response to Fusarium oxysporum infection. G. fasciculatum reduced the disease severity and promoted plant growth significantly (P<0.05) in single-treated and in combination with F. oxysporum-treated plants compared with control plants. The results suggested that G. fasciculatum is a potentially effective protection agent against F. oxysporum.