Fungi are one of the most important groups of marine microorganisms used to produce important enzymes and antimicrobials. Industrially, the cellulase produced from marine fungi plays an impotent role; however, using it medically is very limited. Hence, this study aimed to use purified and characterized cellulase enzymes produced from Geotrichum candidum strain Gad1 to determine their antimicrobial and antifouling activities. The maximum cellulase activity was achieved (55.54 U/ml) with maximum specific activities (325.8 U/mg). The highest antimicrobial activity of cellulase was 42 mm diameter of zone inhibition found against Vibrio damsel as antibacterial, and19 mm diameter of zone inhibition observed against Aspergillus niger as an antifungal. By using 600 ul/l of cellulase, the high reduction of the bacterial load in the formed biofilm was shown. The data obtained during the present study confirmed the potential of fungal cellulase. The cellulase enzyme produced by G. candidum strain Gad1 demonstrated promising antibacterial, antifungal and antifouling properties.