This paper presents the design of a reconfigurable microstrip slot-coupled patch reflectarray using RF MEMS switches. The reflectarray is designed on two back-to-back bonded glass substrates front side of which contains the microstrip patch antenna elements and the backside contains the phase shifting elements. The phase shifting elements consist of microstrip lines the lengths of which are adjusted with MEMS switches resulting with adjustable phase characteristics of each antenna element. A transmission line based model is used to model the unit element of the array which is used to obtain a phase design curve and the design is verified with HFSS. The 4×1 array is then designed at 26 GHz to verify the phase design curve and according to the HFSS simulations, the main beam of the array is rotated by 14° by reconfiguring the length of the microstrip transmission lines with RF MEMS switches.