To provide a jig for testing in-plane shearing capable of accurately and simply measuring the in-plane shearing characteristics of a sheetlike material.

The jig for testing in-plane shearing has a first holding member 12 for holding a test piece T comprising a sheet material along a predetermined straight line direction and a second holding member 22 for holding the test piece T along the direction parallel to the predetermined straight line direction. Parallel force is allowed to act on the test piece T by relatively moving the first and second holding members 12 and 22 in parallel to each other to subject the test piece T to in-plane shearing deformation. At this time, the direction of parallel force is kept constant in the vicinity of in-plane shearing deformation.