Abstract: To investigate the influence of the inclusion effect of cyclodextrin-based materials on the properties of plant active substances, a ferulic acid (FA)-nicotinamide (NIC) co-crystal/hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex was prepared, and the inclusion effect of HP-β-CD on the FA-NIC co-crystal and the solution properties were studied. Phase solubility curves and Job’s curves showed that the FA-NIC co-crystal formed an inclusion complex with HP-β-CD in a 1:1 molar ratio. XRD and infrared spectroscopy results indicated that hydrogen bonding interactions existed between the FA-NIC co-crystal included in the hydrophobic lumen of HP-β-CD and the hydroxyl groups of HP-β-CD. Due to the hydrophobic interactions between the C-H groups and glycosidic bonds in the hydrophobic lumen of HP-β-CD and the FA-NIC co-crystal, FA exhibited higher ultraviolet absorption and fluorescence intensity. Compared with pure FA, the equilibrium solubility in water, ultraviolet light stability, and DPPH radical scavenging rate of FA in the FA-NIC/HP-β-CD inclusion complex were increased by 6.7 times, 17.9%, and approximately 2 times, respectively.