With the steady increase in litter sizes, artificial rearing is becoming widely used to raise surplus piglets. The study aimed to evaluate the potential impacts of artificial rearing on behaviour and immune function in piglets. A total of 240 piglets were divided into three groups: piglets reared by the sow until weaning on day 35 (CON group), piglets artificially reared from day 7 (AR7 group), and piglets artificially reared from day 21 (AR21 group). Behavioural observation was conducted for 8 hours weekly, and the elimination position was recorded on days 7, 21, and 35. Serum and hair samples were collected to measure immunoglobulins and cortisol concentration, respectively. The results revealed that piglets in the AR7 group exhibited less frequent milk-drinking, exploring, and playing, but more frequent belly nosing and oral manipulation of conspecifics. Moreover, artificial rearing affected the elimination sites of AR7 piglets on day 21, but this phenomenon was not observed on day 35. In addition, the AR7 piglets had higher levels of cortisol and CRP, as well as lower levels of IgG and IgA compared to the CON piglets. The AR21 piglets also had a higher CRP level compared to the CON piglets. In conclusion, artificial rearing, initiated either from day 21 or day 7, negatively affected behavioural expression and immune function. Artificial rearing from day 7 was found to be the most physiologically detrimental. • Artificial rearing from both day 21 and day 7 is a stressful event. • Artificial rearing increased abnormal behaviours of piglets. • Sows play a role in establishing the elimination area of their offspring. • Artificial rearing adversely impacts immune function of piglets. [ABSTRACT FROM AUTHOR]