The extract of mangosteen fruit hull has been found to have strong antioxidant activity. However, it has low solubility in aqueous solution. Thus, we incorporated the extract of mangosteen hull (EMH) into a nano-sized carrier, particularly nanofibers. The objective of this research was to fabricate cellulose acetate (CA)/gelatine nanofibers embedded with EMH using the electrospinning technique. CA/gelatine/EMH precursor solution was spun at various flow rates of 0.1, 0.2, and 0.3 mL/h yielding nanofibers with average diameters of 525 (CGE1), 640 (CGE2), and 698 (CGE3) nm, respectively. An antioxidative assay using the DPPH method indicated that all samples (EMH, CGE1, CGE2, and CGE3 nanofibers) exhibited strong antioxidant activity, whereas the smallest nanofibers had the lowest antioxidant activity. Moreover, the XRD pattern of composite fiber (CGE2) implied that the electrospinning process altered the structure of EMH. Furthermore, in vitro release study of CGE1, CGE2, and CGE3 nanofibers indicated a rapid release pattern of EMH from the nanofibers. The rate of EMH released from the fiber was related to the fiber diameter, with smaller fiber facilitating a faster release rate of the EMH. Therefore, the results provide a promising approach to enhancing the solubility and bioavailability of mangosteen fruit hull extract, potentially expanding its therapeutic applications.