The present invention discloses a battery charging circuit adjusting a charging voltage or a charging current according to a battery temperature, which includes: a power stage circuit including at least one power transistor switch and converting input power to charging power by operating the power transistor switch within a temperature range, wherein the charging power includes the charging voltage and the charging current; a reference signal generator obtaining signals representing the battery temperature and generating a reference signal accordingly; and a control circuit generating a switch signal according to the reference signal for operating the power transistor of the power stage circuit, wherein the charging voltage or the charging current is gradually increased as the battery temperature increases in a lower range within the temperature range or gradually decreased as the battery temperature increases in a higher range within the temperature range.