Kappaphycus alvarezii is one of the natural resources containing high carbohydrate, and it has potential as an alternative raw material for sugar industry. This study aims to analyze the optimum conditions of the fungi Trichoderma harzianum in degradating polysaccharides from K. alvarezii into sugar. The seaweed was collected in Takalar Sea, South Sulawesi, Indonesia. The fungi was previously activated at 30°C for three days in 2% of seaweed substrate. The efficiency of the T. harzianum in producing biosugar was evaluated under various concentrations of inoculum (5%, 10%, 15% and 20%) and hydrolysis time (0 h, 24 h, 48 h, and 72 h). The result implied that K. alvarezii contain 55,58% of carbohydrate which was dominated by starch 35.83% and cellulose 12.21%. Furthermore, the highest content of sugar indicated by 12,27 g/L of reducing sugar was obtained at the combination of 20% of the fungi and 24h incubation. In conclusion, the fungi T. harzianum has ability to convert carbohydrate of K.alvarezii to sugar through hydrolysis process.