A path integral formulation by the generalized coherent states of the Thouless parameterization is presented to apply to molecular systems. Explicit expressions of the ensemble average of the physical property including the spin space is also derived. In order to compute the ensemble average, a novel calculating scheme is shown. The Monte Carlo method by the metropolis algorithm is used, and in order to avoid the negative sign problem, a reweighting method is attempted. Simple examples are examined to demonstrate performances of calculations. We discussed in relation to the total energy and the number of the division for the partition function or the temperature. (C) 1997 American Institute of Physics.