The article provides a comprehensive study of the idiostyle and linguistic personality of Saken Seifullin as key factors in the formation of the national style of Kazakh literature in the 20th century. Based on an anthropocentric approach, the article reveals the multi-layered structure of the writer's idiostyle, which includes the lexical-semantic level, conceptual dominants, and pragmatic strategies of text generation. Special attention is paid to the ethnocultural origins of S. Seifullin's figurative system, which reflect the traditional worldview of the Kazakhs and the specifics of the steppe cultural space. The author analyzes the use of folklore elements, ethnographic vocabulary, symbols, mythopoetic images, and paremiological models, which provide a nationally marked poetics in his works. The work traces the interaction of folklore tradition and modernization trends, which allowed S. Seifullin to create an original artistic and linguistic system and make a significant contribution to the standardization of the literary language. The writer's role in shaping a new conceptual sphere of Kazakh literature based on the synthesis of cultural constants (el, zher, erkindik, enbek) and ideas of social renewal is revealed. It has been shown that S. Seifullin's idiostyle is an important link in the process of the formation of Kazakh literary speech, and his activities contributed to the strengthening of cultural and linguistic identity and the formation of stable figurative models of the national style. The article is of interest to researchers in the fields of linguistics, literary studies, ethnolinguistics, and cultural studies, and can also be used in educational practice when studying the history of the Kazakh language and literature.