This research aims to investigate how EFL students' experiences with QuillBot influence their beliefs about its effectiveness as a grammar checker. Using a qualitative exploratory study, in this research I interviewed 5 participants. The participants are fifth-semester students of the English Education Department at a university in Semarang, Indonesia. The criteria for the participants were: 1) using Quillbot for at least 6 months, and 2) using Quillbot to check grammar. Data were collected through Google form questionnaires and interviews through Google Meet, then analyzed using thematic analysis based on the aspects of TAM. The results showed that EFL students had a significant belief in the effectiveness of using QuillBot in identifying grammar errors. This research gives us an overview that QuillBot is effective in identifying and reducing grammatical errors in students' academic writing. Future researchers can explore further research on the use of QuillBot such as the effectiveness of the AI detector feature, whether the feature is really able to detect AI writing or not reliable.