Abstract: In this study, the extract was tested for in vitro activity against oxytetracycline-resistant V. harveyi. Toxicity of the methanolic extract was evaluated by Brain Shrimp Lethality test. Geodia sp. was characterized by three spicula types (oxeas, trianes and oxyaster euaster), encrusting growth formation, hispid surface features and skeletal structure of paratangential ectosome. The methanolic extract of Geodia sp. exhibited anti-oxytetracycline-resistant V. harveyi activity with MIC of 31.25 μg mL^-1. The extract also was able to inhibit the growth of oxytetracycline-resistant V. harveyi in broth culture at concentrations of 1 and 2xMICs and able to kill almost V. harveyi cells at 4xMIC. Interestingly, the extract did not show any toxic effect in Artemia salina up to 125 μg mL^-1. It is the first report for the antibacterial activity of methanolic extract of Geodia sp. against oxytetracycline-resistant V. harveyi, a pathogenic bacterium in marine aquaculture. This results suggest that Geodia sp. might be used as a source of alternative compound to control marine bacterial pathogen especially oxytetracycline-resistant V. harveyi.