Powdery mildew is a widespread and economically important disease on many crop plants like okra, carrots, beets, squash, tomatoes, cucumbers, radishes, etc., caused by one of the prime phytopathogen Podosphaera xanthii. In this study, crude metabolites of halophilic fungi Alternaria alternata were used against the P. xanthii in dose dependent manner, and different concentrations like 50, 100, 150, 200, and 250 mg mL^-1 were analysed by disc diffusion method. Among them, high antifungal activity of 16 mm in diameter was exhibited by 250 mg concentration. Based on the study, it is put forth that halophilic fungi from extreme environments produce highly stable active constituents, which can be utilized to replace the chemical fungicides.