  We study the effect of both Z and Z'-mediated flavor-changing neutral
currents (FCNCs) on the $ lambda_b arrow lambda l^+l^- (l = mu, tau) $ rare
decay. We find the branching ratio is reasonably enhanced from its standard
model value due to the effect of both Z and Z'-mediated FCNCs, and gives the
possibility of new physics beyond the standard model. The contribution of
Z'-boson depends upon the precise value of the mass of Z' boson.

High Energy Physics - Phenomenology