Numerous techniques of preparation have been reported for the encapsulation of the core material, but the microemulsion technique is the most effective and commonly used for encapsulation. In this article, three microemulsification devices including ultrasonic stirrer, labo ratory reactor, and mechanical stirrer were used to produce the alginate nanocapsules containing peppermint oil. The effect of different parameters on surface morphology, mean particle size, and size distributions were investigated. The results indicated that the ultrasonic stirrer is the best device to make the nanocapsules containing essential oils prepared by microemulsion method, so that the size of nanocapsules prepared by ultrasonic stirrer was about 56 nm. Also, the results of GC-MS, FTIR, and TGA show that quantities of the remaining compounds in nanocapsules prepared by ultrasonic stirrer are higher than other devices. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41904.