A boost circuit includes an inductor (L), a MOS transistor (Q), and a number “n” of switch components (Q1-Qn) is disclosed. A first end of the inductor (L) receives an input voltage (Vin), and a second end of the inductor (L) connects to a drain of the MOS transistor (Q). A source of the MOS transistor (Q) is electrically grounded, and a gate of the MOS transistor (Q) is driven by one square-wave signals (S). The number “n” of switch components respectively connects to the inductor and respectively outputs a number “n” of output voltages. The number “n” of switch components are driven by a number “n” of square-wave signals (S1-Sn). A duty ratio of the square-wave signals (S) is d, and the duty ratios of the square-wave signals (S1-Sn) are d1-dn. Before a turn-off time of each period of the MOS transistor (Q), the number “n” of square-wave signals (S1-Sn) are driven by a number “n” of switch components (Q1-Qn) in turn. Wherein d1+d2+d3+ . . . +dn=1−d, and n is an integer greater than one. In addition, a LED backlight driving circuit and a liquid crystal device having the above boost circuit are disclosed.