Headspace single‐drop microextraction with in‐drop derivatization coupled with reversed‐phase high‐performance liquid chromatography method has been developed for the determination of trace level acetaldehyde in polyethylene terephthalate pellets. The headspace microextraction step involves simultaneous extraction, concentration and in situ derivatization of acetaldehyde with 2,4‐dinitrophenylhydrazine. Various factors influencing the performance of headspace single‐drop microextraction, such as extraction solvent, drop volume, temperature and time for extraction, were studied and optimized. The calibration curve was found to be linear over the concentration range of 0.14–3.0 ppm with correlation coefficient of >0.999. The limits of detection and quantitation were 0.07 and 0.14 ppm, respectively. The spiking recovery of acetaldehyde was in range of 103.1 to 105.5%. The method shows good repeatability, with a relative standard deviation of 5.6%. The residual acetaldehyde content estimated in the polyethylene terephthalate pellets by headspace single‐drop microextraction was found to be in agreement with the result obtained by standard ASTM F2013 headspace gas chromatography method. The developed headspace single‐drop microextraction is robust, sensitive and easy to implement in any laboratory.