We conducted this study to investigate the effect of culture depth of red algae Gracilaropsis persica on the growth and biomass production of this species. Three culture depth of 5, 6, and 7 m were used to cultivate algae in the Persian Gulf (Bandar Abbas) for 45 days. Algae was collected from its natural environment and cultivated on polyethylene rope in the sea. We measured relative growth rate (RGR) and total biomass every two weeks. Temperature, salinity, pH, and nutrients (nitrate, nitrite and phosphate) were measured during the trial. The results showed significant differences in growth rate between different treatments (P<0.05). Algae cultivated at a 7 m culture depth had the highest relative growth rate. At the end of the 45-day trial, total biomass was highest in the 7 m treatment (P<0.05). The results of the present study showed that culture depth affected the growth of red algae Gracilariopsis persica.