The catalytic synthesis from transesterification of dimethyl carbonate (DMC). and 1-pentanol (1-PeOH) over alkaline ionic liquid 1-butyl-3-methylimidazolium hydroxide ([bmIm]OH), as well as the optimal reaction conditions, was studied. Results showed that [bmIm]OH exhibited high activity and when the reaction time was 4 h, catalyst dosage was 2.0%, n(DMC):n(1-PeOH) was 1:4, and the dipentyl carbonate (DPC) yield was up to 75.81%. After the alkaline ionic liquid [bmIm]OH was used 5 times repeatedly, the catalytic activity still remained at 94%.