The vaccine hesitancy developed during the COVID-19 pandemic has spread the disease, delayed immunity, and increased death rates. Social media platforms have contributed to the spread of doubts, misinformation about vaccines. Twitter, being one of the most popular social networks in Türkiye, has become a significant platform for vaccine polarization. This study aims to examine the reasons for vaccine hesitancy and conspiracy theories developed by Turkish users on Twitter. 3939 tweets were analyzed with the hashtags #aşıyahayır (#notovaccine), #aşıolmayacağım (#Iwillnotgetvaccinated), #denekolmaTürkiye (#donotbeatestsubjectTürkiye), #aşıolmakistemiyorum (#Idonotwanttogetvaccinated). The examined categories are as follows: scientific (the highest number of comments in this category were related to medical side effects), miscellaneous (the highest number of comments were about the lack of mentioning reasons for vaccine hesitancy), conspiracy theories (the highest number of comments were about major pharmaceutical companies), and general content (opinions against administering Covid-19 vaccines to children).