This paper presents a technique for collimating a diverging beam from a laser diode using a graded-index multimode optical fibre. The theory of the method and some experimental results are presented. Based on geometrical optics, the light propagation formula in the graded-index optical fibre is developed and then the length of the fibre for collimating is determined. The experimental results demonstrate that a laser beam of a large angle of divergence (in the range of 10° to 35°) can be reduced to a fully collimated beam with an angle of divergence of less than 0.04°. The integrated device that consists of the laser diode and graded-index fibre can be used as a light source for optical testing