Abstract: The activity of agarase depended on the bacterial growth conditions such as growth medium formula. In this study, we used marine bacterial strain Brevundimonas sp. DT-7 as an extracellular agarase producer and optimized the growth medium formula to produce maximum agarase that can be used for producing oligosaccharides from agar on a commercial scale in the future. Eight components in the bacterial culture medium (X₁ agar powder，X₂ NaCl, X₃ FePO₄，X₄ CaCl₂，X₅ K₂HPO₄，X₆ FeSO₄·7H₂O，X₇ yeast extract， X₈ peptone) were selected for the optimization. Plackett-Burman design was used in the experiments and the significance of each component (X₁-X₈) contributing to activity of agarase (Y₁) was determined. The significant levels were defined at P<0.05. The data show that among the eight components, three medium components (X₁ agar powder, X₄ CaCl₂ and X₈ peptone) are significant factors for production of agarase from DT-7. The three significant factors (X₁ agar powder, X₄ CaCl₂ and X₈ peptone) were selected for further analysis using Box-Behnken design. A regression model was obtained by response surface regression method (SAS 8.2) as follows: Y₁=499.6+19.45X₁+13.99X₄－1.213X₈－33.16X₁²－5.3X₁X₄－3.45X₁X₈－39.64X₄²－10.23X₄X₈－15.79X₈². The results demonstrate the optimum culture medium components (w/v): 0.536 % agar powder, 2.5% NaCl, 0.1% FePO₄, 0.052% CaCl₂, 0.1% K₂HPO₄，0.03% FeSO₄·7H₂O, 1% yeast extract, and 0.484% peptone, respectively. Using those optimized culture components and combined with other culture conditions ［50 mL culture medium in 250 mL flask, initial pH 7.5, shaken at 120 r/min, incubated at （23±1）℃ for 28 h］, the agarase activity of 503.3 U/mL was obtained, which was significantly higher than that of 372.0 U/mL when the culture medium was not optimized. We conclude that (1) using SAS software is a very effective and quick way to optimize a bacterial growth culture medium; (2) the culture medium optimized in this study is simply formulated and can be used for production of high activity of agarase at low cost; (3) with further modification and improvement, Brevundimonas sp. DT-7 can be a source bacterium for production of agarase on a commercial scale. This is a preliminary study. Further research will be required to evaluate Brevundimonas sp. DT-7 in commercial application.