An auto-focusing method and a digital image processing apparatus using the same are disclosed. The auto-focusing method includes: setting a reference noise level if an illuminance of a photographing area is larger than a predetermined reference value, and setting a variable noise level that varies according to the illuminance of photographing area if the illuminance of photographing area is smaller than or equal to the predetermined reference value; calculating a focus value of each position of the focus lens while driving the focus lens within the predetermined lens-driving range in the unit of a step and selecting a maximum focus value of the predetermined lens-driving range among the calculated focus values, wherein in the calculating of the focus value, the noise level is subtracted from a pixel data that is larger than the noise level and the result of subtracting is used as the pixel data to calculate the focus value.