A recommended, simple and sensitive method for the spectrophotometric determination of diclofenac sodium drug (DLC) in pharmaceutical formulations was represented in this work. The method is based on the coupling of DLC with diazotized 4-Aminoacetophenone in basic medium to form an intense yellowish-brown colored diazocoupling product that showed maximum absorbance at 362 nm. The effect of various factors such as amount of the reagent, time of the reaction and order of addition were investigated. The experimental results indicated a good linearity (r2 = 0.9954) over a concentration range of (2- 40) µg/L with a detection limit of 0.447 µg.L-1 diclofenac sodium under the optimized conditions. The pharmaceutical excipients did not exhibit any interferences. The low value of the standard deviation alongside good correlation coefficient confirms the applicability of the method. Accordingly, the proposed method has been successfully applied to the determination of diclofenac sodium in pharmaceutical formulations. The results were statistically compared with standard methods by means of t-test and f-test at 95% confidence level with no significant differences observed.