The present invention relates to a hydraulic valve lash adjuster which is capable of storing a large quantity of oil therein and exhibits high resistance to wear. In the valve lash adjuster in accordance with the invention, the plunger comprises an upper plunger portion and a lower plunger portion, and the upper and lower plunger portions are welded together with the partition member so that the partition member is sealingly fixed within the plunger. Accordingly, the upper and lower plunger portions are welded together, and simultaneously the partition member is sealingly fixed within the plunger. The plunger thus formed is surface hardened by quenching or carburizing. With the above construction of the invention, therefore, the hardness of the outer surface of the plunger is not impaired and the residual stresses generated by welding do not degrade the resistance to wear and fatigue.