BACKGROUND: Diabetes and hypertension care require effective communication between healthcare professionals and patients. Training programs may improve the communication skills of healthcare professionals but no systematic review has examined their effectiveness at improving clinical outcomes and patient experience in the context of diabetes and hypertension care. METHODS: We conducted a systematic review of randomized controlled trials to summarize the effectiveness of any type of communication skills training for healthcare professionals to improve diabetes and/or hypertension care compared to no training or usual care. We searched Medline, Embase, CINAHL, PsycINFO, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews (CDSR), ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform from inception to August 2020 without language restrictions. Data on the country, type of healthcare setting, type of healthcare professionals, population, intervention, comparison, primary outcomes of glycated hemoglobin (HbA1c) and blood pressure, and secondary outcomes of quality of life, patient experience and understanding, medication adherence and patient-doctor relationship were extracted for each included study. Risk of bias of included studies was assessed by Cochrane risk of bias tool. RESULTS: 7011 abstracts were identified, and 19 studies met the inclusion criteria. These included a total of 21,762 patients and 785 health professionals. 13 trials investigated the effect of communication skills training in diabetes management and 6 trials in hypertension. 10 trials were at a low risk and 9 trials were at a high risk of bias. Training included motivational interviewing, patient centred care communication, cardiovascular disease risk communication, shared decision making, cultural competency training and psychological skill training. The trials found no significant effects on HbA1c (n = 4501, pooled mean difference -0.02 mmol/mol, 95% CI -0.10 to 0.05), systolic blood pressure (n = 2505, pooled mean difference -2.61 mmHg, 95% CI -9.19 to 3.97), or diastolic blood pressure (n = 2440, pooled mean difference -0.06 mmHg, 95% CI -3.65 to 2.45). There was uncertainty in whether training was effective at improving secondary outcomes. CONCLUSION: The communication skills training interventions for healthcare professionals identified in this systematic review did not improve HbA1c, BP or other relevant outcomes in patients with diabetes and hypertension. Further research is needed to methodically co-produce and evaluate communication skills training for chronic disease management with healthcare professionals and patients.