The aim of the current study was to analyze the active ingredients and to screen the pharmacological properties of freshwater laver, Prasiola japonica, the only species grown in Korea. According to results of gas chromatography- mass spectrometry assay, components from P. japonica were more diverse than those from sea laver. Of particular interest, our results indicated that ethanol extract of P. japonica (PJE) contained loliolide, sorbitol, mannitol, and alverine, which were known to have an anti-oxidant, anti-oral microbial, osmotic diuresis, and smooth muscle relaxant, respectively. In addition, five solvent fractions of PJE (water, butanol, chloroform, ethyl acetate, and hexane) significantly inhibited the production of lipopolysaccharide-induced nitric oxide and a higher amount (>100 μg/mL) of chloroform, ethyl acetate, and hexane fraction were considered to play a specific role in cancer cell death. PJE and its solvent fractions found to be effective scavengers of free radicals, particularly, hydroxyl radicals. Glucose uptake in L6 myoblast cell line that stably expresses the glucose transporter type 4 (GLUT4) proteins was also remarkably enhanced upon treatment with solvent fractions, remarkably chloroform fraction. Taken together, we concluded that P. japonica may have potent pharmacological properties and thus contribute to development of novel natural candidates for various disease targets.