Open access (OA) to scientific information is an important feature of the current scientific publishing. Many research funders mandate open access to publications written as part of the projects they support, and they are also willing to cover the costs of these publications in the OA (so-called article processing charges – APC). Due to the increased number of articles published through OA journals, as well as the practice of archiving manuscripts in OA digital repositories, the total number of OA articles is continuously growing. According to the data from the Web of Science Core Collection, at least 45 % of all papers indexed in 2021 are available in OA. Among publishers who publish exclusively open access journals and charge publication fees, MDPI publishes the largest number of papers. Publisher’s propulsive business policy is the subject of controversy at an international level, but the number of their journals and papers published in those journals and indexed in international bibliographic databases is increasing rapidly. Only in 2021, MDPI launched 86 new journal titles, and in the same year, they published 235,638 articles, almost one third of the total number of articles published throughout their 25-year existence (Fig. 1). In this article, we focus on the impact of MDPI on a small scientific community – the Croatian one. Constant increase in the number of articles published by Croatian authors in MDPI journals indexed in WoSCC is shown in Fig. 2. Substantial increase of the share of MDPI articles in the total Croatian scientific production in journals indexed in WoSCC, and in the total number of articles in journals available in OA is given in Fig. 3. In 2021, more than a fifth of all papers by Croatian authors indexed in the WoSCC was published in MDPI journals, representing a third of all Croatian OA papers published in the respective year. We have compared these data for Croatia with the data for Slovakia, Austria, and Finland. While Slovakia shows an even larger increase in the share of articles published by MDPI journals in the period 2019–2021, the impact of MDPI on Austrian and Finnish research community is somewhat lower. Still, a constant increase in the share of articles published in MDPI journals is noticed in all scientific communities analysed (Fig. 4). According to available data, 48 % of the aforementioned papers published by Croatian authors in 2021 were written as part of projects funded by Croatian institutions, but the data on OA publication costs and funding sources are not publicly available. Transparency of these data, which could be provided through the Croatian scientific bibliography CROSBI, would be useful in planning the activities of national financial authorities, as well as for a more successful cooperation with publishers.