Abstract: A window opening and closing assembly capable of controlling an opening angle of the window effectively is disclosed. The assembly comprises a base with a groove along a longitudinal direction thereof, a slider inserted in the groove, an arm rotatably mounted on the base, a handle rotatably placed at a portion of the base and having a worm gear at an end thereof, a worm wheel meshing with the worm gear, and a switch for controlling the location of the slider. Wherein the slider has an angled side inwardly angled at a side of the first sliding portion thereof and the arm has a straight side for restricting a rotation angle thereof. Thus, an opening angle of a window can be controlled by an operation of the straight side and angled side.