Provided is a photobioreactor for mass-culturing marine microalgae using a semi-permeable membrane. The photobioreactor installed in a floating type on a water level or soaked at a predetermined depth from the water level to mass-culture isolated marine microalgae includes a culturing bag formed of the semi-permeable membrane through which enables seawater to exist, but prevents the marine microalgae from being penetrated, the culturing bag being configured to provide a three-dimensionally culturing space for accommodating the marine microalgae and a floating unit connected to the culturing bag to dispose the culturing bag near the sea level, thereby exposing the culturing bag to sunlight. Since the photobioreactor for mass-culturing the marine microalgae using the semi-permeable membrane is provided, the photobioreactor may be manufactured at a low cost and free from the spatial restrictions, thereby enabling the expansion of the photobioreactor in both the horizontal and vertical directions.
