||Traustochytrids spp. was isolated from cultured adult small abalone, Haliotis diversicolor supertexta. It is more frequently to isolate this fungus from abalone in low water temperature season than that of high water season. In histopathologic study, macrophages-engulfed fungus-like spores were noted in the interstitial tissues associated with hepatopancreas, intestine and kidney. This type of lesions was prominent in abalone samples collected in low water temperature season, and this finding correspond to the isolation of fungus. In transmissible electron microscopy, fungus spore-like organisms deposited in the macrophages were evident. One DNA fragment was cloned from cultured fungus using PCR technique, however, it is unable to identify the fungus species from its sequence. Treatment of pond water using antifungal chemical was unable to increase the servility of juvenile abalone in the hatchery.