The robot-driven walking therapies with body weight support (BWS) are recently gaining appreciation as they can improve gait recovery in stroke survivors. However, BWS could evoke a response of the autonomic nervous system (ANS) that could be dangerous in patients with cardiovascular regulation deficit. The aim of this study is to evaluate the ANS response during BWS phases through spectral and symbolic analyses of short-term heart rate variability. This evaluation could help to tailor robot-driven walking strategies preventing discomfort and improving rehabilitation. A group of 10 normal subjects was studied during several BWS phases. Results from spectral and symbolic analyses indicated a gradual sympathetic activation together with a parasympathetic inhibition with increasing percentages of BWS. However, since changes appear mainly as trends, our findings suggest that the progressive increase of the BWS generates a light sympathetic stimulation.