Critical temperatures and pressures were measured for five binary mixtures (DMC + n-hexane, DMC + n-heptane, DMC + n-octane, DMC + n-nonane and DMC + n-decane) and two ternary mixtures (DMC + n-hexane + n-octane and DMC + n-heptane + n-decane) covering whole composition interval. The critical properties were obtained from observing the critical opalescence. The standard uncertainties of temperatures and pressures are no more than 0.65 K and 0.016 MPa. The critical temperature and pressure curves of binary mixtures are continuous, belong to type I or type II defined by Scott and van Konynenburg. DMC + Alkane (n-heptane, n-octane and n-nonane) mixtures show minimums in critical temperature curve. The Redlich-Kister equations are used to correlate the critical properties for binary mixtures. The critical data for ternary mixtures are correlated with the Cibulka's equations and Singh's equations.