BACKGROUND: To overcome the deficiency of pure starch in film-forming performance, ionic liquids (ILs) have been introduced when preparing a homogeneous blend of starch and fiber. It is essential to select the appropriate ratio of starch to fiber and evaluate the film-forming property of the resulted composites. In the present study, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) was used to prepare composites of soybean fiber (SF) and corn starch (CS) at various ratios. The gelatinization properties, water holding capacity, expansibility and film-forming properties of CS-SF composites were measured. RESULTS: The results showed that the composites had good water holding capacity and expansibility. They easily dissolved in water to form a low-viscosity solution, which contributed to improve their film-forming performance. Furthermore, the addition of SF improved the mechanical and barrier properties of the film, and composites with higher SF content exhibited excellent film pliability that remained flexibility even after 30 days of storage. CONCLUSION: The findings demonstrate that the ratio of corn starch to soybean fiber will affect the film-forming properties of the composites formed in [EMIM]Cl. The CS-SF composite film with a CS to SF ratio of 1:1 exhibited the best overall performance. The performance improvement of these CS-SF composite films may be attributed to the molecular entanglement or intermolecular interaction between starch and fiber. These findings provide valuable information for the development of degradable starch-fiber composite films. © 2024 Society of Chemical Industry.