The world is facing the COVID-19 pandemic that has impacted economies and millions of people worldwide. The fact that COVID-19 is highly contagious from person to person has greatly affected the daily lives of people, and it has also had a devastating effect on many sectors, particularly the tourism industry. In order to mitigate losses for the tourism sector and for it to gain a new dynamism under the current pandemic conditions, monitoring and analyzing online reviews is an important factor for better understanding the needs and desires of customers. The purpose of this study was to determine the main topics in online reviews by foreign guests staying in İstanbul during the pandemic period using text mining techniques. The information obtained as a result of the analysis is important in terms of understanding how to manage the current situation, developing suggestions for solutions, improving service quality, making future decisions, and adapting to the new normal.