Eriobotrya japonica (Thunb.) Lindl. (loquat) has been reported to possess various health benefits. Phytochemical studies have identified flavonoids and triterpene acids in its stem bark; however, its biological potential remains underexplored. This study aimed to evaluate the in vitro antibacterial and in vivo antidiarrhoeal activities of the 96% ethanol extract of Eriobotrya japonica stem bark as a candidate natural antibacterial and antidiarrhoeal agent. The extract was prepared by maceration using 96% ethanol and subjected to phytochemical screening. Acute oral toxicity was assessed in Wistar rats according to OECD Guideline 423 using three animals per step. Antibacterial activity was evaluated using the disc diffusion method against Staphylococcus aureus and Escherichia coli at concentrations ranging from 25 to 500 mg/mL (n = 3). Antidiarrhoeal activity was assessed in male BALB/c mice at doses of 200–600 mg/kg BW (n = 4) using a castor oil-induced diarrhoea model. The extract was found to be practically non-toxic at doses up to 5,000 mg/kg BW. Concentration-dependent antibacterial activity was observed against both bacterial strains, with the highest concentration producing the largest inhibition zone against E. coli (12.17 ± 0.61 mm; p 0.05). In the antidiarrhoeal assay, the extract at 200 mg/kg BW showed the most pronounced inhibitory effect on wet faeces and total faecal output, with an inhibition percentage of 83.14%, exceeding that of loperamide. Higher extract doses did not enhance the antidiarrhoeal effect. These findings suggest that Eriobotrya japonica stem bark extract has potential antibacterial and antidiarrhoeal activities with a favourable acute safety profile, although further phytochemical standardisation and mechanistic studies are required.