We synthesized carbon nanotubes (CNTs) from sucrose solution, used as a carbon source, by the liquid-phase arc discharge method, which generates electric sparks between metal electrodes. The quality of the CNTs depends on the molar concentration of sucrose solution because the discharge characteristics vary with its viscosity. When a lower density solution, 0.5 mol/L in this study, was used, the G/D ratio of the generated CNTs was the highest. This result implies that discharge characteristics dependent on solution density play an important role in CNT synthesis in liquid-phase arc discharge. We also examined other saccharides (fructose, glucose, lactose, and maltose) as carbon sources. The results indicated that only sucrose molecules provide CNT precursors.