Abstract: The invention provides a fiber testing device for thermomechanical testing of fibers which preferably includes a linear step motor coupled to a first fiber gripping jaw. A second fiber gripping jaw is positioned in linear relation to the first gripping jaw and is coupled to a load cell. Advantageously, the apparatus includes a chamber for maintaining a fiber test specimen in a substantially thermally isolated environment during testing of the fiber. A heating means and a cooling means are connected to the chamber. The heating means and cooling means are controlled by a control means which also controls the position of the linear step motor. The fiber testing device of the invention is capable of performing complicated mechanical and thermal fiber testing protocals without operator involvement except for initiation of the testing sequence.