This paper presents a vector control sliding mode control (SMC) scheme in the field weakening (FW) region with optimal flux based algorithm. The observation of the rotor flux and stator flux components are also included. This work proves the advantages of vector controlled IM for high performance application in the industry. The vector control ability for easy FW and full voltage and current utilization of inverter fed IM to ensure a wide range of sufficient speed and torque operation was investigated in this work. In a sensorless vector controlled IM, the speed must be estimated using voltage and current components. The parameter variations is the main problem in the high speed operation of IM so that, the sensorless speed estimation through SM technique in the FW region with optimal flux measurement is presented. Space vector pulse width modulation (SVPWM) voltage source inverter is utilized in the algorithm. The simulation results shows the effectiveness of this algorithm at all speed range of operation.