A serial-type LED device includes p light source units and a dimming circuit. Each light source unit includes first and second terminals, m light strings and m current balance units. Each light string includes LEDs coupled in series to have a first terminal coupled to the first terminal of a corresponding light source unit and a second terminal coupled to the second terminal of the corresponding light source unit through a corresponding current balance unit. The first terminal of the first light source unit is coupled to a second DC voltage, and the second terminal of the i-th light source unit is coupled to the first terminal of the (i+1)-th light source unit, where m and p are integers greater than or equal to 2 and i is any integer from 1 to (p−1). The dimming circuit coupled to the second terminal of the p-th light source unit controls the second DC voltage according to a current outputted from the p-th light source unit.