The division and circadian DNA-synthesis rtythm are studied in chick liver immediately after hatching. The vision function is tested by the mitotic and the $^3H-thymidine$ labelling index The DNA synthesis exhibited a cyclic variation of 12 hours immediately after hatching. The rhythmic changes of DNA synthesis was maintained in the liver of meal-fed chickens, but the DNA synthetic activities decreased gradually in the starved chicken liver. From this time, the rhythm of DNA synthesis was greatly afffected by lighting schedule, all these DNA synthesis of chicken liver was accompained by mitosis.