A water-soluble conjugated polymer, poly[lithium 5-methoxy-2-(4-sulfobutoxy)- 1,4-phenylenevinylene] (MBL-PPV), spontaneously forms nanoparticles at flat mica surfaces. In this work, we manipulated single PPV nanoparticles with a modified version of AFM, our recently developed vibrating scanning polarization force microscopy (VSPFM). VSPFM provides a new way to obtain undistorted imaging of "soft" molecules at surfaces. We have demonstrated that we could stepwise compress a single PPV nanoparticle with an AFM tip and estimate its compression elasticity in a small force regime.