An image sensor comprises an active pixel region that includes a plurality of unit pixels arranged in a matrix pattern, a first optical black region formed adjacent to the active pixel region, wherein a plurality of shaded unit pixels are arranged therein, a drain region formed adjacent to the first optical black region, the drain region discharging excess electrons generated in the active pixel region, and a second optical black region formed adjacent to the drain region, wherein another plurality of the shaded unit pixels are arranged therein.