The Minimal Quark-Lepton Symmetry Model and the Limit on Z'-mass

A minimal extension of the Standard Model containing the four-color quark-lepton symmetry is proposed and discussed. The existence of a rather light extra $Z'$-boson originated from the four-color quark-lepton symmetry is shown to be compatible with the current electroweak data. The cross sections $\sigma(e^+ e^- \rightarrow \gamma, Z, Z' \rightarrow \bar f f)$ are calculated, and their deviations from the SM predictions are shown to be significant at $\sqrt s \ge 200 GeV$ and available for the measurements at the LEP200 and future colliders.