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Aims Diseases of maricultured species caused by Vibrio harveyi are increasing in China and other regions. This study examined the genetic diversity, antimicrobial susceptibility, plasmid profiles and virulence potential of the V. harveyi isolated from marine organisms farmed in two provinces in eastern China between 2014 and 2019. Methods and Results A total of 54 V. harveyi were obtained from seven marine species. Enterobacterial repetitive intergenic consensus (ERIC)‐PCR fingerprinting revealed substantial genetic heterogeneity among the V. harveyi isolates. There was no significant correlation between ERIC‐PCR genotypes and host origins or fish farms. All the isolates were resistant to amoxicillin and ampicillin, and 79·6% to kanamycin. We found that 61·1% of the V. harveyi isolates had plasmid(s) and there were 14 different plasmid profiles. Most isolates from fish hosts (76·5%) contained plasmids; however, 75% of isolates from nonfish hosts lacked plasmids. Experimental infection results showed that isolates with plasmid(s) were more virulent to large yellow croaker than isolates lacking plasmids (P < 0·05). Conclusions This study confirmed that V. harveyi isolates obtained from animals farmed in the coastal region of east China were genetically diverse. Our results suggest that the virulence of various V. harveyi strains to fish is associated with the plasmids they carry. Significance and Impact of the Study More than 50% of the V. harveyi isolates carried one to 11 plasmids. The plasmid‐borne traits of V. harveyi strains might be important for host adaptation and virulence, but they were not associated with susceptibility to the tested antibiotics.