This article focuses on the structure of phraseological units in the Romanian and English languages via a contrastive study. The author looks into the phraseological antonyms by studying the lexical nature of their components. A classification of this type of antonyms into four groups has been devised while introducing various linguistic perspectives. Generally speaking, antonymy is more frequent within the lexical and phraseological units that signifies abstract notions of space, volume, qualities, quantities, notions of time, objects and phenomena in the material world, notions labeling human activities, feelings, will, desire, the human state, etc. Comparable to the lexical antonyms, the phraseological antonyms belong to the same lexical and grammatical class, namely they are in a correspondence relation with the same parts of speeches: verbs, adjectives, adverbs and nouns. Our research has proven that the phraseological antonyms are usually in a correspondence relation with the verbs , adjectives and nouns and rarely with adverbs.