  The S, T, U parameters in the $ SU(3)_C\times SU(3)_L\times U(1)$ model with
right -handed neutrinos are calculated. Explicit expressions for the oblique
and Z - Z' mixing contributions are obtained. We show that the bilepton oblique
contributions to S and T parameters are bounded : $- 0.085 \stackrel{<}{\sim} S
\stackrel{<}{\sim} 0.05$ and $- 0.001 \stackrel{<}{\sim} T \stackrel{<}{\sim}
0.08$. The Z - Z' mixing contribution is positive and above 10%, but it will
increase fastly with the higher Z' mass. %can be negative. The consequent mass
splitting of the bilepton is derived and to be 15%. The limit on the mass of
the neutral bilepton in this model is obtained.
