This article aims to research common and different aspects of affirmative and negative sentences in Uzbek and Turkish languages. First of all, the problem of definition and interpretation of words in Uzbek and Turkish linguistics, which express the meaning of affirmation and negation in the compared languages, was studied. Then the adverbs and compounds that form negative sentences in both languages were compared and studied. In some situations, it is noted that the form of affirmative sentences expresses the negative meaning, and negative sentences express the affirmative meaning. That is, it was observed that in the affirmative and negative sentences of the compared languages, semantic-formal inconsistency sometimes appeared in the structure of the text. The article uses the methods of analysis, comparison, synthesis, generalization, description. As a result of the research, the common and different features of grammatical additions and tools forming affirmative and negative sentences in Uzbek and Turkish languages were studied. Also, the means of forming affirmative and negative sentences, which ensure the inconsistency of affirmation and negation from a semantic and formal point of view, are described.