We study the friction behaviors of poly(vinyl alcohol) (PVA) gel sliding against glass surface in dilute poly(ethylene oxide) (PEO) aqueous solution with various molecular weights, Mw, and concentrations. At low sliding velocity (10-5, 10-4 m/s), distinct PEO polymer effects are observed: The frictional stress in PEO 2E4 (Mw = 2 × 104 g/mol) solutions is lower than that in pure water, decreasing with the increase in PEO concentration and reaching a minimum at the crossover concentration, c*. However, in higher molecular weight solution, PEO 4E6 (Mw = 4 × 106 g/mol), this friction reduction effect is only observed for very dilute concentration (0.01c* solution), and the friction stress in higher concentration (0.1c*, 0.3c*, and c* solution) is higher than that in pure water, accompanied by the appearance of “plateau”. At fast sliding velocity (10-2, 10-1 m/s), all the friction curves in dilute PEO solution superpose with the curve in pure water, independent of Mw and concentration of PEO. These results in...