Radiofrequency ablation (RFA) method is an effective method in cancer surgery. However, due to its high temperature and pressure, explosive behavior called 'steam popping' was occurred during RFA. This phenomenon can cause recurrence and metastasis of the cancer. Though this is a critical problem, but steam popping still can be detected by the explosive sound. In this research, thin film based flexible pressure sensor with the range of 100 - 400 kPa was developed, and attached to the RFA needle to monitor the steam popping through pressure variation. Fabricated needle showed low interference from temperature variation, electromagnetic noise, and chemical environment noise. Proposed needle successfully monitor the steam popping phenomenon.