A commercial engineering polymer of polyetherimide (ULTEM), a liquid crystal copolyester (TLCP), and blends with different percentages of TLCP in ULTEM have been rheologically analyzed in this work. Rheological measurements have been performed both at low and high shear rates. In particular, by means of a cone and plate rheometer, the transient shear flow behavior has been studied. The time necessary to reach the steady stress value was much longer in the case of the TLCP than for the amorphous ULTEM. Steady state rate sweeps as well as dynamic sweeps have been also carried out and discussed. Moreover, data obtained at high shear rates revealed that ULTEM viscosity is possibly pressure dependent. A procedure is shown for correlating the results obtained with the different techniques. The possibility of improving the processability of ULTEM has been also studied. In this regard the effect of the addition of low percentages of TLCP on the rheological properties of the thermoplastic matrix has been analyzed.