aloysia triphylla, also known as lemon verbena is a medicinal plant with aromatic leaves which produce essential oil rich in citral and has great importance for pharmaceutical and cosmetic industries. the objective of this study was to evaluate the effect of frost on the chemical composition and yield of a. triphylla essential oil. the experiment was conducted at the campus of ufsm in frederico westphalen, rio grande do sul, in july 2014. a complete randomized design with three repetitions was used where three random collections and extractions occurred before and after the occurrence of frost. the oil was obtained via hydrodistillation and analyzed by a process of gas chromatography and mass spectrometry. the total yield obtained from leaves before frost was 0.162% and 0.187% after frost. essential oil composition was largely not affected by the presence of frost; however, of the macro components, limonene was observed to be most sensitive to frost, accounting for 14.36% of essential oil content before and 10.15% after frost. key words: chemical composition, secondary metabolites, low temperatures.