AbstractIn this paper, a new force transmission index called the mean force transmission index (MFTI) is proposed, and the force transmissibility analysis procedure is established for parallel manipulators. TheMFTIis an extended definition of the force transmission index (FTI) introduced by the authors previously. It is shown that theFTIis a function of the input velocity ratio (IVR) for a multi‐DOF mechanism of the same configuration. To represent the force transmissibility by a definite value, theMFTIis defined as the mean value of the normalizedFTIs function over the whole range of theIVR. The force transmissibility analysis of two planar parallel manipulators is illustrated using theMFTImethod. The result is compared with that of the Jacobian matrix method and the joint force index (JFI) method. It shows that, especially for symmetric parallel manipulators, an approximate inverse‐proportionality relationship exists between theJFIandMFTI, and between the maximum input torque/force andMFTI. It is concluded that theMFTIcan be used as a quantitative measure of the force transmissibility performance for parallel manipulators. In the end, a design optimization problem is studied by taking the global force transmission index as the objective function. © 2003 Wiley Periodicals, Inc.