Abstract: A new interior window locking system for preventing intruders from gaining illegal entry into a building. The inventive device includes a pair of horizontally disposed guide rails secured above and below a window within a window frame. A pair of square tubing frames are slidably disposed between the guide rails. Each of the frames have a steel grate disposed therein. A spring-loaded latch assembly is disposed on corresponding inner members of the pair of square tubing frames for engagement thereof.