Measurements of the thermal expansion and hence the coefficient of thermal expansion are reported for alloys (x = 0, 5, 8, 10, 12, 16 and 25%) in the temperature range of 300 to 1300 K using a dilatometer. Room temperature x-ray diffraction studies show that for %, a small fraction of Re begins to precipitate out, in addition to the dominant face-centred cubic (fcc) phase whose lattice constant increases linearly with x. The variations of with x plotted at selected temperatures of 503, 903 and 1203 K shows that for %, decreases with increasing x at 503 and 903 K, whereas it remains practically constant with x at 1203 K. The latter result is in agreement with the predictions of Mei et al (1994 Alloy Modeling and Design ed G M Stocks and P E A Turchi (Warrendale, PA: TMS Publishing)) using molecular dynamics simulations. The variation of with x shows a minimum at x = 12% at all temperatures. The possible role of shear stresses in the dendritic grain structure of these alloys on measured below 1000 K is discussed.