This thesis investigates if the announcement of lockdown had a significant impact on stock market return in Denmark. The research approach used is quantitative and deductive and the sample consists of ​​daily adjusted close prices of stock from the 20 largest listed companies in Denmark, according to market capitalization rate. The time period studied is 28th of February 2020 till 27th of March 2020. Lockdown's effect on stock market return is studied using a Difference-in-Difference model, where daily adjusted close prices of stocks from the 20 largest companies in Sweden are used as a control group.  The COVID-19 pandemic has for the past two years had a huge impact on societies globally. At the beginning of the COVID-19 outbreak, to try and stop the spread of the virus, governments around the world implemented lockdowns of varying degrees. Denmark was one of the first countries to implement lockdown. However, the culturally and market similar Sweden, opted for a different approach and did not implement a lockdown at all. It is therefore of interest to investigate whether lockdown announcements had a measurable impact on stock returns at the beginning of the COVID-19 outbreak. Previous research conducted by Vasileiou (2020), Baker (2020), Ichev and Marnič (2018), Hassing Nielsen & Lindvall (2021) and Ashraf (2020) on the subject have found that COVID-19 generally contributed to market uncertainty. This uncertainty in turn affected the stock market significantly, both positively and negatively. The major findings of this thesis suggest that the lockdown implemented in Denmark had no significant effect on stock returns during the investigated sample period.