PURPOSE: To characterize a polymer molecule and the like effectively by a method comprising a step for placing particles in a medium, a step for applying an external force temporarily to the particles, a step for causing a physical variation of the particles, and a step for measuring the variation using a microscope.

CONSTITUTION: Particles are characterized by placing individual particles including deformable and undeformable particles in a polydisperse sample, applying an external force to the Particles, causing a physical variation, in particular in the conformation and position, and then observing the variation. This method is useful for characterizing polymer molecules of various dimensions including a smallest particle being detected through an appropriate microscope (which can be coupled arbitrarily with a spectroscopic analyzer in order to detect a molecule too small to be visualized) and a large molecule having length of several inches when it is developed in linear conformation.