Model adsorption structures of polyamide (poly(E-caprolactam)) on graphite surfaces which have been proposed from a scanning tunneling microscopy (STM) study were examined by molecular dynamics (MD) simulations using a short oligomer as a model molecule. The model. structure for loose chain packing was thermodynamically (and locally) stable in the simulation, whereas that for close chain packing was unstable. Moreover, the former structure was globally unstable to a finite size (chain spacing) disturbance, and a transition to the structure with a different chain alignment direction on the graphite surface occurred. As a result, in contrast with the STM study, the simulation results suggested this structure with a 0.47-nm chain spacing and chain directions of the [11 ($) over bar 20] direction of the graphite surfaces as the most probable absorption structure. Possible reasons for this contradiction were discussed. For the close chain packing structure, no model structure could be obtained from the simulations.