RBP4, also known as retinol-binding protein 4, is the specific carrier for retinol, and is responsible for the conversion of unstable and insoluble retinol in aqueous solution into stable and soluble complex in plasma through their tight interaction. This protein delivers retinol from the liver stores to the peripheral tissues. In plasma, the RBP-retinol complex interacts with transthyretin and prevents its loss by filtration through the kidney glomeruli. Recombinant mouse RBP4, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.