The present invention provides packings for high performance liquid chromatography whose residual silanol groups are extremely reduced and which remarkably prevent tailing of basic compounds. Endcapping agents represented by the following general formula [II] are reacted in liquid phases or gas phases with silica gel which is surface-modified with chemical modifying agents to link the endcapping agents to the residual silanol groups on the silica gel surface. In the formula, R³ and R⁴, the same or different, are alkyl having one to four carbon atoms, and n is the factor of structural unit and an integer of 2 to 10. ##STR1##