Blends of poly(butylene terephthalate) (PBT)/high density polyethylene (HDPE)/ionomer (IONO) polymers, at a blending ratio of 76/19/5 (by weight), were reinforced with short glass fibres (GFs) at levels of 10-30 wt% in order to enhance the mechanical properties for load-bearing engineering applications. The melting and crystallization behaviour of the composites, studied by differential scanning calorimetery (d.s.c.), indicate the presence of an increase in crystallinity in the presence of the glass fibres. Dynamic mechanical thermal analysis (d.m.t.a.) shows that the introduction of glass fibres reduces damping to a greater extent than would be expected theoretically. Incorporation of glass fibres increases the storage modulus, when compared to the unreinforced system, at all temperatures studied. The presence of short glass fibres increased the melt viscosity and decreased the extrudate swell, with the effect being more pronounced at higher temperatures. Rheological data have been analysed on the basis of fibre length (or aspect ratio) and/or distribution of the fibre lengths by using the rheological model proposed by Maron and Pierce.