Lanthanum(III) supported on the magnetic mesoporous organosilica nanoparticle (La@MON) has been described as an efficient, simple, and durable heterogeneous catalyst for the synthesis of 5-membered cyclic carbonates from carbon dioxide (CO2) and epoxides. Under optimized reaction conditions, various terminal epoxides have been converted to the corresponding carbonates in the presence of 0.3 mol% La@MON and 0.5 mol% tetrabutylammonium iodide (TBAI) as co-catalyst at relatively mild reaction conditions. It was also found that La@MON catalysts had significantly higher catalytic activity than some selected reference catalysts, which can be explained by the abundance of lanthanum(III) species acting as Lewis acidic sites for activating both carbon dioxide and epoxide molecules, along with the fact that the catalyst channels are short and provided facile mass transfer. The catalyst showed good reusability for at least five reaction cycles while the magnetic core of the catalyst helps the easy separation of the catalyst by just using an external magnet.