A tensile testing instrument of the soft type which has been specifically designed to facilitate accurate axial alignment of submicron whiskers or filaments is described. The load is applied by a dead‐weight loading mechanism similar to that used in chain balances and strain is measured photographically. The limiting feature on the accuracy of the results is the diameter variation which occurs within individual whiskers rather than the instrument. Tensile data are presented for a 0.35‐&mgr;‐diam Cr fiber extracted from a unidirectionally solidified ingot of Cu‐Cr eutectic alloy.