Development of new and highly sensitive colorimetric method for the determination of pipazethate hydrochloride, fenoterol hydrobromide and clopidogrel hydrogen sulphate based on aggregation of the citrate capped gold nanoparticles (Au NPs). Citrate-capped gold nanoparticles were prepared by chemical reduction of HAuCl4 using citrate as the reducing agent and stabilizer. The synthesized nanoparticles showed an intense localized surface plasmon resonance absorption band at 520nm. Uniformly distributed spherical gold nanoparticles with average particle diameter size of 14.20±2.53 nm were verified through Transmission Electron Microscope (TEM). Addition of the cited drugs to the Au NPs solution results in aggregation of the Au NPs. As a result of aggregation, the plasmon band at around 520 nm disappears with the formation of a new red shifted band at 647- 674nm. The calibration curves were linear with concentrations of 0.4-0.8, 0.8-2 and 1.6-9.6 μg/ml for pipazethate hydrochloride, fenoterol hydrobromide and clopidogrel hydrogen sulphate, respectively. The detection limits were 0.100, 0.061 and 0.259 μg ml-1 for pipazethate hydrochloride, fenoterol hydrobromide and clopidogrel hydrogen sulphate, respectively. The method was applied successfully to the determination of the cited drugs in pure form and pharmaceutical dosage forms.