We observed a micro-Brownian motion of single molecules of a chiral helical pi-conjugated polymer as a molecular spring on mica substrate under n-octylbenzene at room temperature using high-speed (rapid scan) AFM. The average velocity at the chain end of the polymer was 67 nm s(-1) at the observation point. The analytical result shows that the mean square displacement in a single polymer chain is proportional to the time and, hence, complies with Einstein's law of Brownian motion. The diffusion constant (D) is measured to be 8.2 x 10(-15) m(2) s(-1) at the solid/liquid interface.