Introduction: The sequelae of Bell's palsy may mean that it persists for up to six months because of incomplete recovery from paralysis. This randomized controlled trial aimed to investigate the clinical effectiveness of thread-embedding acupuncture (TEA) compared with a sham control in the treatment of patients who had Bell's palsy for longer than 3 months. Methods: A randomized, parallel-controlled, patient-assessor blinded clinical trial was conducted. In addition to concurrent acupuncture treatment delivered twice a week for eight weeks, the intervention group also received TEA, and the control group was given sham TEA once a week for eight weeks. The primary outcome was change in the Facial Disability Index (FDI) from baseline to eight weeks. The secondary outcome was change in FDI from baseline to four weeks, changes in House-Brackmann grade, Facial Nerve Grading System 2.0, Sunnybrook Facial Grading System, facial stiffness, lip mobility, and satisfaction score. Results: Of the 61 patients enrolled in the study, 56 were included and randomized. There was a significant difference in the FDI physical score in the TEA group compared with that in the STEA group at eight weeks (p = 0.048). Lip length index in the TEA group was significantly better than that in the STEA group at four weeks (p = 0.014). There was no significant difference for other outcome measurements. Conclusions: The results showed that the addition of TEA to standard acupuncture treatment was not statistical significant in terms of total FDI. Despite partial clinical improvement, further research is needed for the effectiveness of TEA.