Among the forts and ramparts which are remaining from the Seljuks period, Jalali Castle in Kashan city has a special feature. Today ,a part of its walls is visible justly. By king Jalal al din Malekshah of Seljuk's command, this fortress was built in Kashan southwest for maintain Kashan security and consequently safeguarding of comerical roads and Seljukid capital namely Isfahan. This article based on the humanities studies and reviews of the sources and also process of urban developments in Kashan, analyses that how to build Jalali Castle and its ending. The result of the research shows, this Castle that, for centuries, protected from a unsafe sideline in South of Kashan ,was known along with the moat and rampart of city and after the Kashan expansion and connection of roads of city towards the North and West, and also for the sake of human destructions ,was damaged and vanished walls and a ditche connected to the Castle.