In this paper, sulfonic acid functionalize magnetic starch (denoted Starch/SPION@SO3H) is fabricated by the polymerization of 4‐styrenesulfonic acid on the surface of magnetic starch. Magnetic starch (Starch/SPION) is synthesized by covalent modification of starch by silica capsulate superparamagnetic iron oxide nanoparticles (SPION). For this purpose, Starch/SPION is modified by allyltrimethoxysilane, follows by the polymerization of 4‐styrenesulfonic acid onto this material. The catalyst is characterized by various characterization techniques, including transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), vibrating‐sample magnetometer (VSM), X‐ray photoelectron spectroscopy (XPS), and acid/base titration. The characterizations prove the structure of Starch/SPION@SO3H catalyst. The catalytic activity of Starch/SPION@SO3H is evaluated in the multicomponent reaction of 4‐hydroxycoumarin, benzaldehydes, dimedone, and ammonium acetate for the synthesis of chromeno[4,3‐b]quinoline‐6,8(9H)‐dione derivatives. The catalyst shows very good activity in the synthesis of chromeno[4,3‐b]quinoline‐6,8(9H)‐dione derivatives. Several benzaldehydes with electron donating or electron withdrawing functionalities are used as starting material and all the substrates give the desired products in high isolated yields. In addition, the catalyst is extremely reusable during 10 sequential runs. Characterization of Starch/SPION@SO3H catalyst by TEM, VSM, and acid/base titration after recovery from the reaction proves the stability of the catalyst in the reaction conditions.

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