BACKGROUND: Clinically rocuronium, a muscle relaxant, has no significant inhibitory effect on the autonomic nervous system in the healthy population. However, there has been no study done on rocuronium in diabetic patients. Therefore, we used heart rate variability (HRV) as a biomarker to investigate cardiac autonomic function after rocuronium administration to diabetic patients. METHODS: In 21 diabetic adult patients, heart rate (HR), mean arterial blood pressure (BP), low frequency (LF, 0.04-0.15 Hz) power, high frequency (HF, 0.15-0.4 Hz) power, LF/HF ratio, SD1 and SD2 in the Poincare plot before induction of anesthesia, and immediately before and after rocuronium administration were calculated and compared. RESULTS: HR, mean BP, LF, LF/HF ratio and SD2 after rocuronium administration did not differ significantly from the measurements taken before rocuronium administration. HF and SD1 decreased significantly after rocuronium administration (P = 0.022, P = 0.019 respectively). Covariates such as age, gender, weight, duration of diabetes mellitus and hypertension did not alter the effect of rocuronium on the autonomic nervous system. CONCLUSIONS: Rocuronium produced a significant decrease in parasympathetic activity. Therefore, further study will be needed to determine whether vagal reduction caused by rocuronium could have potential to deteriorate hemodynamics in diabetic patients.