Tape casting was modified in order to align the silicon nitride whiskers in the silicon nitride slurry. Based on a simplified fluid dynamics model, it was understood that torque for aligning the whisker was increased by n(2) times by dividing the flow into n narrow ones. Samples with 3 wt % silicon nitride whiskers of a hexagonal crystal structure were prepared by using three different tape casting methods; conventional tape casting, tape casting modified by using an array of razor blades, and tape casting modified by using an array of sharpened pins. The razor blades of 13 mm in length were 5 mm apart from each other in the array, and the sharpened pins of 0.08 mm in diameter 0.7 mm apart from each other in the array. Samples were fully densified by gas pressure sintering. Both the sintering shrinkage anisotropy and X-ray diffraction analysis showed that the sample prepared by employing the pins had the best whisker alignment among the three samples.