Abstract: In order to track the target bacteria effectively, fluorescein isothiocyanate(FITC) was used as the marker to study the effect of labeling concentrations(0.2, 2, 20, 50, 100, 200 μg/mL) and time(1, 15, 30, 60, 120, 240 min) on the fluorescence intensity of V.anguillarum labeled FITC.In the meanwhile, the stability of fluorescence labeled on V.anguillarum stored at different temperatures(25, 4, -20, -70 ℃) and different time(24, 48, 96, 192 h) were compared.The possible change of fluorescence intensity was monitored when V.anguillarum labeled FITC was inactivated by formaldehyde.Also the fluorescence quenching effects of different intensity natural light(0, 150, 1 500, 25 000 lx) indoors and the effects of repeated freezing and thawing at -20 and -70 ℃ on V.anguillarum labeled FITC were analyzed.The results showed that the optimal concentration of FITC was in the range of 20 to 100 μg/mL and the optimal time was in the range of 60 to 120 min.The fluorescent signal from V.anguillarum labeled FITC was more stable when it was stored at -20 and -70 ℃ than those stored at 4 and 25 ℃.The stability of fluorescent signal from formaldehyde inactivated V.anguillarum labeled FITC was better than that from the control, and no difference was found in the quenching effect in different intensity of natural lighting.After 3 times of freezing and thawing, the fluorescent signal from V.anguillarum labeled FITC frozen at -70 ℃ was more stable.The results above provided useful technical parameters when FITC was used as a marker to label the marine bacteria.