Background: A validation study is needed to make domestic applications of German Kneipp therapy. Purpose: The study aims to test the effect of a Kneipp therapeutic program in a domestic forest environment on the autonomic nervous system. Methods: The program was made considering the 4 key elements (‘exercise’, ‘regulative therapy’, ‘nutrition’, and ‘phytotherapy’) of the Kneipp therapy. Total 3 sessions (once a week for 5 hours in each session) were performed to 40 domestic adults divided into four groups (10 in each group). HRV was measured on the subjects before and after the intervention, and its 6 characteristic parameters (TP, VLF, LF, HF, LF/HF, CSI: Cumulative Stress Index) were compared for statistical analysis. Results: For 33 subjects excluding 7 who were disturbed by interrupt factors during measurements, significant improvements after the intervention, were observed in TP(8.64%, p < ..001), VLF(6.96%, p < .05), LF(15.86%, p < .001), HF(8.46%, p < .01), LF/HF(5.77%, p < .05) and CSI(−16.06%, p < ..001). Conclusions: The Kneipp therapy performed in the forest environment was shown to activate the autonomic nervous system and in particular the sympathetic and parasympatheric nervous to promote heart activity, and was also shown to most significantly reduce cumulative stress. The present observations would be the first preliminary evidence that the Kneipp therapeutic interventation in a domestic forest environment results in positive responses of the autonomic nervous system including stress relief.