Nowadays, the clean production of bio-based products and fixation of carbon dioxide (CO₂) are highly desirable. In this work, carbonated fatty acid methyl esters have been successfully prepared in 99% yield by cycloaddition of CO₂ with bio-based epoxidized methyl soyates. This was accomplished with a simple and cheap catalyst system of polyethylene glycol 400 (PEG-400) and potassium iodide (KI) under solvent-free conditions. Experimental parameters such as the molar ratio of polyethylene glycol to metal halide, catalyst loading, reaction temperature, reaction time and CO₂ pressure were systematically evaluated. The PEG-400 and KI co-catalysts (4 mol%) could significantly promote the cycloaddition of CO₂ with internal epoxides (epoxidized methyl soyates) to produce carbonated fatty acid methyl esters. FT-IR and NMR analyses were used to confirm the product, and 99% yield of the five-membered cyclic carbonated methyl soyates was obtained at 120 °C with 3.0 MPa pressure of CO₂ for 20 h. This method provides a cleaner approach for the production of bio-based products.