A strong toroidal rotation braking has been observed in plasmas with application of an n = 1 magnetic perturbation field on JET tokamak. Calculation results from the momentum transport analysis show that the torque induced by the n = 1 perturbation field has a global profile. The maximal value of this torque is at the plasma core region (ρ < 0.4) and it is about half of the Neutral Beam Injection (NBI) torque. The Neoclassical Toroidal Viscosity (NTV) torque is calculated in different collisionless regimes. This observed torque profile agrees well with the predicted NTV torque in the v regime with the collisional boundary layer effect included.