Abstract: This invention relates to a derivative of 1-(p-chlorobenzoyl)-5-methoxy-2-methyl indole-3-acetic acid with 3-oxo-1-isobenzofuranyl, linked by an ester bond, more particularly to 1-(p-chlorobenzoyl)-5-methoxy-2-methyl indole-3-acet-3-oxo-1-isobenzofuranyl ester, as well as to its preparation and therapeutical use as an analgesic and anti-inflammatory agent.Said compound is prepared by reacting equi-molecular amounts of 1-(p-chlorobenzoyl)-5-methoxy-2-methyl indole-3-acetic acid and bromophthalide a few hours at room temperature, under a mild stirring, in the presence of a base.