Abstract: A window structure includes a frame, two sliding panels and a locking element interlocking the sliding panels. The frame consists of two horizontal members, two vertical members and an upright middle pillar which interconnects the middle portions of the horizontal members. Each of the horizontal members has two parallel channels on two sides of the middle pillar, along which the sliding panels are slidable. Two endless slots are formed in the window structure on two sides of the middle pillar and are filled with two resilient primary sealing strips respectively so as to establish a liquid- and air-tight seal between the frame and the sliding panels. Two inclined guiding members are mounted in the frame so that the primary sealing strips are compressed gradually between the frame and the sliding panels when the sliding panels are moved from the middle pillar to the vertical members.