The outbreak of coronavirus disease (COVID-19) has posed significant challenges to human wellbeing and survival, particularly among groups of people such as the Sundarbans mangrove forest resource-dependent communities (SMFRDCs), and especially the fishermen in these communities, in developing countries like Bangladesh. It is therefore essential to explore the livelihood conditions, health status and care-seeking behavior of the fishermen in these communities during the ongoing pandemic. This study was carried out by applying mixed methods, including interviews and focus group discussion (FGD), in the three sub-districts of Khulna, Satkhira, and Bagerhat, which are in the southwestern region adjacent to the Sundarbans mangrove forest (SMF) of Bangladesh. Quantitative data were collected from 76 fishermen through telephone interviews, while 24 fishermen participated in three distinct focus group discussions. The findings suggest that the fishermen have experienced a reduction of income, as they have been barred from entering the SMF during the pandemic, which has gradually affected their number of trips to and stays at the forest as well as their catch of fisheries resources. The decline in demand in both regional and international markets has left the fishermen with only a handful of alternative ways to adjust to these unprecedented circumstances, such as borrowing money, selling household assets, and in some extreme cases marrying off young children to reduce the financial burden, as many are now jobless. Their financial hardship during the pandemic has affected their households' capacity to afford basic household necessities, including food, fuel, education, and health expenses. Subsequently, when these fishermen suffer ailments such as fever, cough, headache, and cold – the general symptoms of COVID-19 – they cannot seek medical assistance from trained doctors. Their financial constraints have compelled them to rely on indigenous knowledge, in particular village quack doctors, or in some cases to seek help from local pharmacies for modern medicine. Thus, the government should provide financial support and strengthen the local market value chain so that disadvantaged fishermen in SMFRDCs can adopt alternative livelihood opportunities. Furthermore, longitudinal research on the impacts of COVID-19 on livelihood, local adaptation strategies, health status, and care-seeking behavior is also strongly recommended.