Bracing has been widely used for the treatment of adolescent idiopathic scoliosis (AIS). However, effectiveness of brace treatment remains controversial. A systematic review was conducted to investigate evidence that brace treatment is effective in the treatment of AIS. A total of 20 studies, including randomized controlled trials, nonrandomized clinical controlled trials, or case-control studies, were included. Studies comparing the results of brace treatment with no-treatment, other conservative treatments, or surgical treatment were included. Outcomes of the studies included radiological curve progression, incidence of surgery, pulmonary function, quality of life (QOL), and psychological state. The results from the systematic review are difficult to interpret. There are quite a number of varying parameters between studies that make it very difficult to reach any firm conclusions. In addition, the quality of evidence is limited because most of the studies included in this review were of low methodological quality. However, the available data suggest that, compared to observation, bracing is more potent in preventing the progression of scoliosis and may not have a negative impact on patients' QOL. Therefore, bracing can be recommended for the treatment of AIS, at least for female patients with a Cobb angle of 25-35°. Compared to other conservative treatments, bracing seems to be more effective than electrical stimulation, although an advantage of bracing over side-shift exercise or casting has not been established. Comparison between bracing and surgery is difficult because in most studies, the curve magnitude at baseline was considerably larger in the surgery group. We recommend that future studies have clearer and more consistent guidelines.