[Objective] To aquire compounds with novel structures or potent antimicrobial activities through research on metabolites of endolichenic fungus Elaphocordyceps sp. isolated from Leptogium sp.. [Methods] We confirmed taxonomy status of the endolichenic fungus by PCR amplification, evaluation of the ITS (internal transcribed spacer) sequence of nrDNA, sequence comparision in GenBank Database and construction of the phylogenetic tree. Constitutes were isolated by the gel column chromatography, sephadex LH-20 and HPLC methods. Structures were elucidated by physicochemical properties and spectral data analysis. Double dilution method was adopted to evaluate antifungal activity. [Results] The testing strain was identified as Elaphocordyceps sp.. Three compounds were isolated and purified from the fermentation of the endolichenic fungus. Their structures were elucidated to be ergosterol, 4,8-dihydroxy-1-tetralone and De-O-methyldiaporthin. The three compounds show weak inhibition on Candida albicans sc5314. De-O-methyldiaporthin exhibits very strong phytotoxic activity, with leaf sensitivity concentration of 4 nmol. The concentration of De-O-methyldiaporthin in fermentation broth of Elaphocordyceps sp. reached 0.75 mg/L (3.2′103 nmol), much higher than the leaf sensitivity concentration of 4 nmol. [Conclusion] De-O-methyldiaporthin produced by the fungus of Elaphocordyceps sp. can be a microbial herbicide.