A method for loop detection and a network device applying such method are provided. The method includes: receiving, by a port, a loop detection frame; detecting, by a loop detection unit, whether the loop detection frame is transmitted via a port of the network device; analyzing, by a frame analyzer unit, the loop detection frame when the loop detection frame is transmitted via the port, and determining whether there is any loop in the network device; and shutting down the port of the network device or not perform any action, by a port switching unit when the frame analyzer unit determines that there is a loop in the network device, wherein the loop detection frame is a loop detection protocol data unit (LDPDU) frame.