The present invention describes a process for preparing a cyclooxygenase-2 selective inhibitor. It provides a synthetic procedure for the said substance namely 5-chloro-3-(4-methylsulphonyl)phenyl-2-(2-methyl-5-pyridinyl)pyridine of formula (I). The invention also relates to preparation of a new intermediate of formula (IV) and a process to prepare it. Furthermore, the invention describes a process for preparing another key intermediate of formula (II). Compounds of formula (IV) and formula (II) are useful intermediates in synthesis of the said cyclooxygenase-2 inhibitor.