Herein, the in vivo protective effects of Kappaphycus alvarezii, dried using two different methods, over 5-fluorouracil (5-FU)-induced intestinal mucosal injury were explored. A total of 35 Balb/c mice were randomly divided into five groups: non-treated group (N), placebo treated group (M), treated with 5-aminosalicylic acid (5-ASA) group, treated with sun-dried K. alvarezii (SKA) group, and treated with air-dried K. alvarezii (AKA) group. Intestinal mucosal injury was induced by intraperitoneal injection of 5-FU, and the body weight (bw) and food intake of the mice were recorded daily. After the experiment, the thymus and spleen indexes were calculated. The jejunum histology was evaluated, including the villus length, crypt depth, and their ratio (V/C value). An enzyme-linked immunoassay was performed to detect the serum levels of the tumor necrosis factor (TNF)-α and interleukin-10. Overall, the weight gain rates of all groups were higher than that of the M group (-3.30%, -6.19%, -5.09%> -7.50%). Moreover, the weight and food intake reduction was significantly suppressed by day 3 of treatment (16.85, 16.83, 16.76>15.75 g, and 2.15, 2.18, 2.19>1.54 g). The thymus index of the 5-ASA group (5.92 mg/10 g b.w.) and the AKA group (6.81 mg/10 g b.w.) were slightly higher than that of the M group (5.67 mg/10 g b.w.). Histological analysis showed that, compared with the M group, all treated groups had improved jejunum, with significantly longer villus (332.58, 334.44, 350.75>252.09 μm) (p<0.01). Additionally, the V/C values of the 5-ASA (6.39) and AKA (6.35) groups were much higher than that of the M group (5.12) (p<0.05). Compared with the M group, the AKA group has significantly lower serum TNF-αlevels (470.73<580.69 pg/mL) (p<0.05) and remarkably higher interleukin-10 (306.11>287.41 pg/mL). Altogether, dried K. alvarezii, regardless of the drying methods used, can alleviate the manifestations of 5-FU-induced intestinal mucosal injury in mice.