PURPOSE: To readily separate and purify DNA having each molecular weight by one chromatography treatment, by passing a mixed specimen of DNA having molecular weight in a specific range through a column packed with specific spherical particles.

CONSTITUTION: Spherical particles such as nonporous gel which consists essentially of glucomannan and are nonporous or porous particles having ≤0.01μ pore diameter and have 5-20μ central particle diameter and a particle size distribution in the range of 0.5-1.5 the central particle diameter are packed into a column and a mixed specimen of DNA having molecular weight in a range of 1-100 Kbp is passed through the particle packed layer of the column to readily and efficiently separate and purify each DNA from the mixed specimen.