This experiment evaluated the effects of sugarcane extract (SCE) on growing pigs' diarrhea incidence, serum immunity, intestinal morphology, and antioxidant enzyme activity. A total of 116 52-day-old commercial pigs (Duroc × Landrace × Jiaxing Black, average weight of 11 ± 1 kg) were randomly allocated to control (CON, basal diet) and 1% SCE group (SCEG, basal diet + 1% SCE). The experiment lasted four weeks. Compared with CON, diarrhea incidence (SCEG: 74.11% versus CON: 54.76%) and diarrhea index (SCEG: 83.65% versus CON: 73.61%) dropped largely in pigs supplemented with SCE. Villus height in the duodenum (p < 0.01) and the ratio of villus height to crypt depth (p < 0.05) increased in SCEG. Dietary SCE enhanced the activity of catalase (CAT) capacity, and decreased tumor necrosis factor α, and malondialdehyde levels in serum (p < 0.05). CAT activity in the ileum increased (p < 0.05) in piglets supplemented with SCE. Thus, dietary supplementation with SCE improved diarrhea incidence, serum antioxidant capacity and immunity, and intestinal villus morphology and may be used as an efficient antibiotic alternative in weaned piglet feed.