We studied factors associated with quality of life (QOL) among myasthenia gravis (MG) patients in two university hospitals in Thailand: Thammasat University (TU) and Khon Kaen University (KKU). Consecutive MG patients from an outpatient neurology clinic of both sites were enrolled and their clinical variables and QOL by the Short-Form 36 questionnaire were assessed. There were 31 and 40 subjects enrolled at TU and KKU, respectively. The mean values of the SF-36 score in seven dimensions were higher at the TU site. The significant factors between both sites were mean age, and numbers of participants with myasthenic symptoms and steroid treatment. The frequency of MG symptoms was the only factor associated with the SF-36 score (correlation coefficient -0.66, p value < 0.01). In conclusion, the frequency of MG symptoms might be the main factor that lowers QOL in MG patients in both physical and mental aspects.