  We study the Casimir effect for parallel plates with massless Majorana
fermions obeying the bag boundary conditions at finite temperature. The thermal
influence will modify the effect. It is found that the sign of the Casimir
energy keeps negative if the product of plate distance and the temperature is
larger than a special value or the energy will change to be positive. The
Casimir energy rises with the stronger thermal influence. We show that the
attractive Casimir force between two parallel plates becomes greater with the
increasing temperature. In the case of piston system involving the same
Majorana fermions with the same boundary conditions, the attractive force on
the piston will weaker in the hotter surrounding.
