To explore the method of microchemistry marking on the otolith of Japanese flounder, , during the process of proliferation and release, the juveniles with a total length of (1.56±0.16) cm were immersed at four different concentrations (0.5, 2, 8, and 32 mg/L) of SrCl₂·6H₂O for 72 h to detect the Sr sedimentation effect. During the immersion period, half of the water was exchanged by fresh seawater daily, and SrCl₂·6H₂O were added to maintain constant concentration for each group. The exogenous Sr sedimentation in otoliths was detected by X-ray electron probe microanalyzer (EPMA). Results of line transect analysis showed that the strontium marking on otoliths could not be formed after the immersion of two concentrations (0.5 mg/L and 2 mg/L). The Sr high area appeared in the 8 mg/L concentration group with a 5.49-8.49 peak value, and the mean value of the Sr/Ca (Sr:Ca×1000) ratio was 4.50-6.60. Furthermore, in the 32 mg/L group, the mean value of the Sr/Ca ratio was 6.61±0.86, and the peak value of Sr was 5.62-11.04. This means that otoliths of can be marked with strontium by the method of SrCl₂·6H₂O immersion. However, in the 8 mg/L concentration group there were also unlabeled samples. and the mean value of Sr/Ca was lower than that of the 32 mg/L group. In the 32 mg/L group, the strontium marking rate was 100%, and the mean value of the Sr/Ca ratio was 6.61±0.86, which was significantly different ( < 0.05) compared with that of the control group. The EPMA mapping analysis showed that the red "high strontium marking ring" in the otolith appeared in the 8 mg/L group and 32 mg/L group, and the color of the "high strontium marking ring" was deepened with increasing of concentration. One-way analysis results showed that the total length and weight was not significantly different between the experimental groups and the control group (O immersion did not affect the growth of young fish. A Chi-square test ( > 0.05) showed there were no significant differences in mortality rate among the different concentration groups. Overall, 32 mg/L SrCl₂·6H₂O was the best marker concentration.