Although bariatric surgery (BS) is recognized as an effective strategy for body weight loss, its impact on cardiorespiratory fitness (CRF) is still unclear. We aimed to examine postoperative changes in CRF (VO2max/peak) and its relationship with weight loss among adults undergoing BS. We systematically searched the WoS, PubMed, MEDLINE, and Scopus databases. Observational and intervention studies were selected reporting the presurgery and postsurgery CRF, measured by breath-by-breath VO2 or its estimation. Eleven articles (312 patients) revealed that BS leads to a reduction in absolute VO2max/peak in the short term (effect size, ES = −0.539; 95%CI = −0.708, −0.369; p < 0.001), and those patients who suffered a more significant decrease in BMI after BS also had a greater loss of absolute VO2max/peak. However, VO2max/peak relative to body weight increased after surgery (ES = 0.658; 95%CI = 0.473, 0.842; p < 0.001). An insufficient number of studies were found investigating medium and long-term changes in CRF after BS. This study provides moderate-quality evidence that the weight loss induced by BS can reduce CRF in the short term, which represents a therapeutic target to optimize BS outcomes. More high-quality studies are needed to evaluate the impact of BS on VO2max/peak in the short, medium, and long term including normalized values for fat-free mass.