This study was conducted to investigate the effects of crude Aloe vera polysaccharide (AVP) on the growth performance and immune function of weaned piglets. A total of 200 (Landrace Yorkshire × Duroc) weaned pigs at 21 d with initial 8.88 ± 0.49 kg body weight (BW) were allotted to one of four dietary treatments in a randomized complete block design according to their sex and BW (5 replicates with 10 pigs per pen, 5 gilts and 5 barrows). Dietary treatments included one basal diet, and three diets with AVP supplementation (0.05%, 0.1%, or 0.2%). Average daily gain (ADG), average daily feed intake (ADFI), and feed:gain (F:G) ratios were calculated at the end of the experiment. Separated serum samples from each treatment were assayed at the end of the experiment for the concentrations of cytokines and the blocking rate of antibodies against classical swine fever virus (CSFV). Supplementation of AVP at 0.1% improved (P < 0.05) ADG compared with the control group. No significant differences in ADFI or F:G were observed between AVP-treated and untreated control piglets. All AVP-treated pigs had a significantly lower incidence of diarrhoea (P < 0.05) when compared with control pigs. Feeding AVP resulted in increasing (P < 0.01) IL-2 and IFN-γ (at 0.1% and 0.2%) and IL-4 (at 0.05%, 0.1% and 0.2%), and in no significant changing of IL-10 (P > 0.05). Supplementation of AVP at 0.05%, 0.1% and 0.2% increased (P < 0.01) the blocking rate of antibodies against CSFV. These results indicate that dietary supplementation with dietary AVP enhanced growth performance in weaned piglets by improving immune function, decreasing the incidence of diarrhoea.