  In this Letter we show that in relativistic regime maximally entangled state
of two spin-1/2 particles not only gives maximal violation of the Bell-CHSH
inequality but also gives the largest violation attainable for any pairs of
four spin observables that are noncommuting for both systems. Also we extend
our results to three spin-1/2 particles. We obtain the largest eigenvalue of
Bell operator and show that this value is equal to expectation value of Bell
operator on GHZ state.
