AbstractToroidal field ripple, δ =(Bmax ‐Bmin )/(Bmax +Bmin ), in ITER will be relatively large, about 0.5% at the outer midplane. Due to the importance of toroidal rotation on plasma stability and confinement it is important to understand the consequences of a non‐negligible ripple field on rotation. Guiding centre following Monte Carlo code ASCOT is used to evaluate the torque on plasma from co‐current NBI in presence of toroidal magnetic field ripple. Simulations are made for a JET discharge from 2007 Ripple Campaign aimed to clarify the effect of ripple on fusion plasmas in preparation for ITER. ASCOT results show large reduction of torque from co‐NBI and negative torque from thermal ions, which together could create a counter rotating edge plasma. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)