Intermetallics formation in the Pt-Al binary system at temperatures in the range of 20-600 °C have been investigated by the study of thin aluminium coatings deposited on thick platinum substrates. In order to characterise the changes caused by elevated temperature several techniques such as microscopy, X-ray diffraction, nuclear microprobe techniques and microhardness testing were used. In addition to changes in morphology, the high temperature X-ray diffraction (XRD) analysis showed that the initial phase formed when Pt and Al reacted was Pt2Al3. The formation of Pt2Al3 phase started at 250 °C and it is followed by the PtAl and Pt3Al phases. Furthermore, the Pt-Al intermetallics increased the surface hardness; the process of surface hardening by formation of intermetallics without compromising the purity of pure platinum is of great importance for jewellery and other applications where the properties such as hardness and scratch resistance are crucial.