The flow structure and near field acoustic profile of a supersonic jet at a Mach number of 2.0 and Reynolds numbers of 105 and 106 were investigated by particle imaging velocimetry, schlieren visualization and acoustic measurement using a microphone. The effect of the disturbance in the shear layer was also investigated. In the case of higher Reynolds number jet, the presence of disturbance does not significantly affect the flow and acoustic fields because the shear layer state has already been turbulent even without the disturbance. However, presence of disturbance significantly affects the flow and acoustic fields in the case of moderate Reynolds number jet (Re=105) because the initial condition of the shear layer without disturbance is laminar and disturbance promotes the turbulent transition which has the strong influence on flow and acoustic fields. The sound pressure level decreases with adding disturbance because the promoted turbulent shear layer is smoothly growing instead of rapid growth in the vicinity of the transition which leads to strong acoustic wave emission.