Objective: This study aimed at providing preliminary data useful in reducing participant dropout and improving the quality of clinical trials, by analyzing the factors related to dropout. Methods: The data came from 15 acupuncture and/or moxibustion clinical trials (n=638; August 2005 to December 2009). Logistic regression analysis was used to reveal factors influencing participant dropout. Results: Gender, age, treatment method (intervention), treatment frequency, availability of follow-up, and presence of compensation treatment for the control group were factors influencing participant dropout. Conclusion: Subsequent studies of large-scale acupuncture and moxibustion clinical trials should address dropout factors that consider the character of each clinical trial, or general characters like participants’ gender, age, occupation, and diverse diseases.