This meta-analysis was a systematic review of evidence on the effects of mindfulness-based stress reduction (MBSR) and mindfulness-based cognitive therapy (MBCT) on quality of life (QOL), pain, fatigue, anxiety, and depression in cancer patients. Until July 2020, PubMed, Cochrane Library, and Embase were searched for randomized controlled trials (RCTs). The study included 18 RCTs. The MBSR/MBCT intervention resulted in a significant effect on QOL (SMD 0.80, CI 0.28, 1.32, I2 = 94%). In subgroup analysis, MBSR/MBCT interventions had a significant effect in the early cancer stage on anxiety (SMD − 3.48, CI − 4.07, − 2.88), and QOL (SMD 4.30, CI 3.62, 4.99); in alleviating decreasing pain (SMD − 0.42, CI − 0.70, − 0.14) within 4 weeks after the end of intervention, and alleviating fatigue in younger participants (SMD − 0.64, CI − 1.09, − 0.19). MBSR/MBCT has short-term effects on cancer patients, especially in younger patients and early cancer stages.