ABSTRACT This study investigates the regime-switching effect of the pandemic on the stock market index in Turkey. Daily data from 3 March 2020 to 31 August 2020 is used, four explanatory variables are included and Markov switching regression is applied. The empirical findings indicate that (i) the index has a long-term cointegration with the explanatory variables included; (ii) the new COVID-19 cases, credit default swap (CDS) spreads and foreign exchange (FX) rates are influential in the high-volatility regime, whereas FX rates are not influential in the low-volatility regime and (iii) net buying amounts of foreign investors are not effective in both regimes.