The present invention relates to the identification and characterization of a plant cyclopropane fatty acid synthase and the identification and cloning of the relevant gene sequence. The invention also relates to the use of that gene for the efficient production of cyclopropane fatty acids in an oilseed crop. The invention specifically relates to a cyclopropane fatty acid synthase from a plant in which the major cyclic fatty acids accumulated in the seed are cyclopropane fatty acids.