A non contact laser micrometer was introduced to a conventional single filament tensile testing instrument to directly measure small displacement of stiff fiber samples，allowing strength，modulus and strain of single filaments to be measured simultaneously and accurately.Complicated system corrections were eliminated by using this laser micrometry method.Experimental results obtained from T300 carbon fibers agreed well with the data provided by manufacturer in term of accuracy，a nonlinearity in modulus for the carbon fiber sample was observed during extension，further indicating that laser micrometry method is capable of measuring strain and modulus directly and accurately，especially for high modulus materials.The markers attached to the fiber specimen appeared to be the key to accurate measurements，the effects of the shape,size and material of markers were experimentally studied.It is showed that markers should be opaque with straight parallel sides and perpendicular to the fiber axis.