BACKGROUND: Diabetic cardiac autonomic neuropathy (CAN) is one of the important complications of diabetes. It is characterized by reduced heart rate variability (HRV). METHODS: In this randomized, double-blind, placebo-controlled, multicenter trial, 75 patients were randomly assigned to one of two groups. One group (n=41) received alpha-lipoic acid (ALA) at an oral dose of 600 mg/day for the first 12 weeks and then 1,200 mg/day for the next 12 weeks. The other group (n=34) received placebo treatment for 24 weeks. CAN was assessed by measuring HRVs in people with diabetes. RESULTS: Most of the baseline measures for HRVs were similar between the ALA and placebo groups. Although there were no statistically significant HRV changes in the ALA group compared to the placebo group after 24 weeks of trial, we found a positive tendency in some of the HRV parameters of the ALA group. The standard deviations of normal-to-normal RR intervals in the standing position increased by 1.87 ms in the ALA group but decreased by -3.97 ms in the placebo group (P=0.06). The power spectrum of the low frequency (LF) band in the standing position increased by 15.77 ms(2) in the ALA group, whereas it declined by -15.04 ms(2) in the placebo group (P=0.08). The high frequency/LF ratio in the upright position increased by 0.35 in the ALA group, whereas it declined by -0.42 in the placebo group (P=0.06). There were no differences between the two groups regarding rates of adverse events. CONCLUSION: Although a slight improvement tendency was seen in HRV in the ALA group, there were no statistically significant HRV changes in the ALA group compared to the placebo group after 24 weeks of trial. However, the high oral dose of ALA was well-tolerated.