Force field parameters required for molecular dynamics (MD) simulations can be obtained using quantum mechanical calculations, even if the parameters for a target molecule are unavailable from existing force fields. In the case of macromolecules, the derivation of parameters is difficult because of the high computational costs of the calculations. However, if the macromolecules of interest contain repeating units, the cost can be reduced using the following method. Initially, the parameters for an oligomer consisting of at least 3 repeating units (terminal and internal units) are obtained via quantum mechanical calculations. The parameters for the oligomer are then converted into the corresponding parameters for the polymer (terminal and internal × n units). The conversion from the oligomeric parameters to those of the polymer requires highly complicated multi-step procedures. In the present study, we developed web-based software (o2p) to facilitate the parameter conversion in a semi-automated manner using a simple graphical user interface. Its effectiveness was evaluated by conducting MD simulations for amylose in nonane. Spontaneous folding of amylose into a left-handed single helical structure was observed in the simulation. The resulting structure was in good agreement with experimental results, thereby demonstrating the effectiveness and reliability of o2p.