Neaifield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light transmitted through the sub-wavelength aperture. To solve this problem we report the development of plasmonic nearfield scanning optical microscope with a high optical coupling efficiency. By exciting surface plasmons, plasmonic NSOM probes are capable of focusing light into a 100 nm spot. Both numerical simulation and nearfield exposure experiments have demonstrated that the intensity at the focal point is at least 10 times stronger than can obtained from the conventional NSOM probes under the same illumination condition. By providing a strong nano-scale light source, plasmonic NSOM can be used as a high speed nano-scale imaging tool for cellular visualization, molecule detection, and many other applications requiring high temporal resolution.