Abstract: The present invention provides a line interactive UPS, which comprises an AC input, an AC output, a chargeable and dischargeable device, a DC/AC inverter, a rectifying circuit, a full-bridge inverter, a capacitor, a switch, a charger, a boost circuit and a rectifying and buck circuit. An output of the boost circuit is connected to an input of the full-bridge inverter. The rectifying and buck circuit is controlled to provide a rectified output or a rectified and voltage-decreased output. An input of the rectifying and buck circuit is connected to the AC input. The rectifying and buck circuit is operative to provide a pulsating DC to the boost circuit or the full-bridge inverter. The line interactive UPS of the present invention can provide a stable AC to the AC output and has the advantages of small size and low cost.