Grid computing is a term referring to the combination of computer resources from multiple administrative domains to reach a common computational platform. Mobile Computing is a Generic word that introduces using of movable, handheld devices with wireless communication, for processing data. Mobile Computing focused on providing access to data, information, services and communications anywhere and anytime with all significances. Mobile grids simultaneously are related with traditional grids and mobile computing technologies. This kind of grids inherits all bequests of traditional grid computing and has the trait that supports mobile users and devices in a wireless, Transparent, secure and efficient way. In this paper we suggest a job replica count determiner based on fuzzy inference system to improve mobile grid performance. Simulation results shows that our approach improve parameters like system throughput and network traffic, though job failure rate remains in same condition and mean response time become worse.