A series of molecular dynamics simulations in aqueous solution have been carried out in order to investigate the effects of the length of the peptide chain and the temperature on the helical conformation of un-ionized poly(gamma-D-glutamic acid). The results reveal that the helix is not stable for a small number of residues independent of the temperature. On the other hand, the temperature induces a conformational transition from the helical state to the random coil. Analysis of the energy of the whole system indicates that the helix is more stable than the random coil state by about 5 kcal/mol, even although the solvation potential energy is lower in the latter than in the former.