ABSTRACTSelf‐prepared styrene–isoprene–butadiene rubber (SIBR) was anionically synthesised and modified by a hydrogenation reaction. The hydrogenated SIBR (HSIBR) was used as a viscosity index improver in lubricants due to its improved thermal and oxidative resistance. The precursors and corresponding hydrogenated polymers were characterised by size‐exclusion chromatography, Fourier transform infrared, proton nuclear magnetic resonance (1H‐NMR) spectroscopy, differential scanning calorimetry and thermal gravimetric analysis. Moreover, the efficiencies of HSIBR as viscosity index improvers for SAE 5W‐30 multigrade oils (150N HG base oil) were studied. The results confirm that adding 1 wt.% of HSIBR markedly increases the specific viscosity of base oil, increases the viscosity index (119 for base oil) up to a value between 158 and 164 and maintains the shear stability well. Furthermore, the HSIBR‐containing oil possesses a high high‐temperature and high‐shear viscosity without destroying its low‐temperature fluidity. Copyright © 2012 John Wiley & Sons, Ltd.