AbstractBimetallic NiIr4 and NiOs4 alloy nanoparticles are prepared and studied with regard to their performance in catalytic hydrogenation reactions. NiIr4 and NiOs4 nanoparticles are obtained by oleylamine‐driven reduction and exhibit mean diameters of (8.9±1.3) and (6.8±1.4) nm at low agglomeration. The phase composition was determined in detail by using different methods, which include high‐resolution TEM, scanning transmission electron microscopy, selected‐area electron diffraction, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy. This and results in a uniform distribution of both metals Ni‐Ir and Ni‐Os with a ratio of 1:4. The catalytic performance of the NiIr4 and NiOs4 nanoparticles for hydrogenation reactions is evaluated using three selected model substrates: 1‐octene, cinnamaldehyde, and diphenylacetylene. Similar sized Ni, Ir, and Os nanoparticles were used as references. Most remarkable are the excellent selectivity of NiOs4 in the hydrogenation of cinnamaldehyde and the promising formation of (Z)‐stilbene in terms of conversion activity and selectivity. The alloying of Ir and Os with Ni, moreover, is highly cost efficient. In general, both bimetallic alloy nanoparticles, NiIr4 and NiOs4, are shown here for the first time in terms of synthesis, composition, and catalytic hydrogenation.