摘要： Mefenamic acid belongs to class of drug NSAIDS (non-steroidal anti-inflammatory drugs). Mefenamic acid inhibits the synthesis and actions of prostaglandins and it also block the COX-1 and COX-2 or COX enzyme. The purpose of this research is to study the effect of acid and base by using UV spectrophotometry, on different brands of mefenamic acid under ICH guideline Q1A (R2). According to USP, mefenamic acid contains not less than 98 % and not more than 102 % of C15H15NO2 calculated on dried basis. The result concludes that when chosen brands of mefenamic acid i.e. dolor (A), postron forte (B), mefnac (C), positron (D), garden forte (E) were subjected to 0.1 N HCl (acidic medium), highly considerable degradation were observed in all the brands i.e. D (23.10 %), A (24.46 %), E (34.95 %), B (43.02 %) and C (66.34 %). Similarly when different brands of mefenamic acid were subjected to 0.1 N NaOH, highly considerable degradation were observed in the brand A, B (187.44 % and 124.38 %), C (51.93 %) and no degradation were observed in brand D and E (88.75 %) and (89.09 %). It is most commonly preferred as compare to other methods because of less time consuming and maintenance cost and can be use in routine quality control laboratories.