Sodium alginate can be isolated from brown seaweed which will be used for synthesis of nanocomposite based on nano sodium alginate that is impregnated with inorganic nanoparticle TiO2, so it has an excellent nature that comes from the combination between both characters. Characterization of the synthesis result is conducted by using instrumentation such as FTIR, SEM, TEM, and XRD. The result of nanocomposite based on nano sodium alginate-TiO2 synthesis can be applied as a catalyst to synthesize 5-hydroxymethylfurfural (HMF) from fructose which becomes an important alternative in making biofuel using UV-Visible spectrophotometer characterization at maximum wavelength 284 nm showed by a percent yield. The optimum condition of 5-hydroxymethylfurfural synthesis from 180 mg fructose at 120°C for 60 minutes and 50 mg nanocomposite as catalyst obtained the yield of HMF at 39.57%. The nanocomposites produced in this work is suitable as catalyst for biofuel synthesis such as 5-Hydroxymethylfurfural from fructose.