The problem of a generalized retrofit design of multiproduct batch plants is considered in this paper. Unlike previous research on this topic, which concerns only the ways to add a new unit which will be operated in-phase or out-of-phase with the existing units, we get a better result by altering the existing operating mode between existing units (or between new units). Disposing of the useless existing units and replacing outworn equipment with new are also considered. We present a new generalized superstructure with a concept of ＇group＇, a collection of units operated in-phase, then formulate it as an MINLP problem with an implicit or explicit group expression. Five examples will verify the effectiveness of this method.