A safety buckle for a window blind assembly includes a connecting part, a bar section, and a pair of surrounding arms. The connecting part is adapted for mounting on one side of the window blind assembly, and has two ends spaced apart from each other in a longitudinal direction. The bar section extends along the longitudinal direction and is connected to the two ends of the connecting part. Each of the surrounding arms extends along an arc from a corresponding one of the ends of the connecting part toward another one of the ends of the connecting part. The surrounding arms cooperate with the bar section to define a buckle hole that is adapted for extension of a pull cord unit of the window blind assembly therethrough. The surrounding arms define an escape path therebetween that is in spatial communication with the buckle hole.