The paper deals with changes in the Czech aspectual system during the last twenty-five years. The author analyses data acquired from the Czech National Corpus or, more precisely, from subcorpora containing only journalistic texts (the national daily newspapers Hospodářské noviny, Lidové noviny, Mladá fronta DNES and Právo). The corpus-based analysis showed that the frequency of the verb (and its finite forms) has been increasing in journalistic texts and that the statistic relation between imperfective and perfective verbs, as well as the relation between grammatical tenses in Czech, has become more asymmetrical (especially, the frequency of imperfective verbs has been rising). The increase in aspectual asymmetry accentuates the “western” features of the Czech aspectual system in the sense of S. M. Dickey’s (2000) conception. Together with the increasing aspectual asymmetry in Czech, the frequency of bi-aspectual verbs has slightly decreased. The analysis also showed that the frequency of verbs with prefixes (both perfective and imperfective) has decreased in Czech. The author interprets these facts as results of the transmission of certain dynamic (and system-based) features from spoken language to the written language, and he also discusses the typological context of the changes (inferring aspectual meanings from grammatical context as a manifestation of strengthening analyticity in Czech).