  The gauge coupling constant unification at the low ($O$(TeV)) scale can be
obtained just in four dimensions, without help of the power like
renormalization group evolution in extra dimensions, due to the presence of
some extra particle states at intermediate scales. We show explicit examples of
such extra states in the range of 100 GeV -- 1 TeV which can be easily observed
on future colliders and can have important impact on the particle
phenomenology. The problems of the low scale grand unification and proton
stability are also discussed.
