INTRODUCTION: An electromagnetic field is a factor that people are exposed to constantly, from various sources. Thus, the interest in its influence on living organisms increases. AIM(S): The aim of this work was to investigate the long‑term effects of an extremely low frequency electromagnetic field 50 Hz (ELF-EMF) on stress-related behaviour. METHOD(S): Adult male Wistar rats were exposed to ELF‑EMF of two values of magnetic induction: 1mT and 7mT. Animals were exposed to ELF‑EMF 1 or 8 hours a day for 7 days. Behavioral changes were evaluated in the open field test, which was performed in 1mT groups immediately or 5 weeks after the exposure, and in 7mT groups immediately, 5 weeks, and additionally 9 and 13 weeks after the exposure to ELF‑EMF. Control rats were subjected to the same experimental procedure as the respective animals exposed to ELF‑EMF except electromagnetic field exposure. We also included in the procedure the non‑treated and then exposed to the open field rats (sham). RESULTS: The behaviour of the animals exposed to 1mT did not differ significantly in comparison to control groups, regardless of the time of exposure. In 7mT groups, we found changes in stress behaviour and their intensity increased with increasing exposure time. In addition, the ELF-EMF-induced effect persisted longer in the case of the group exposed for 8 hours compared to animals exposed for 1 hour. CONCLUSIONS: On this basis, we concluded that ELF-EMF of 7mT may act as a stress factor, and its long‑lasting effects depend on the time of exposure. Furthermore, the absence of significant differences in the case of 1mT ELF‑EMF may indicate the existence of certain compensatory mechanisms in the organism, which allows them to avoid a negative influence of the weak electromagnetic filed. FINANCIAL SUPPORT: Research supported by grant from National Science Centre, Poland, no. 2017/25/B/ NZ7/00638 and project no. POWR.03.05.00‑00‑Z302/17 Universitas Copernicana Thoruniensis In Futuro, a part of the programme Knowledge Education Development.