Alkali isomerization of methyl linoleate by sodium hydroxide in ethylene glycol to prepare conjugated linoleic acid was explored. A conversion of methyl linoleate of 92.4 % and a yield of conjugated linoleic acid of 89.3 % were obtained under the optimum reaction conditions of m(sodium hydroxide): m(methyl linoleate): V(ethylene glycol) = 1: 5: 7.5 at 170 oC for 4 h. The advantages for the new alkali isomerization of methyl linoleate instead of linoleic acid are the low-cost for commonly used potassium hydroxide being replaced by sodium hydroxide, the low consumption of alkali as methyl linoleate instead of the facilely saponified linoleic acid, and the diminished consumption of ethylene glycol since the mass transfer is easy for less saponification initially occurred.