The purpose of this study was to examine the influence of the lunar phases and lunar brightness on cardiac autonomic function (CAF) in healthy individuals. A total of 177 healthy individuals were included in the study. All individuals underwent 24h ambulatory electrocardiography (Holter monitoring). Four groups were used at different phases and brightnesses of the moon. Cardiac sympathetic and parasympathetic activity was assessed using heart rate variability (HRV). Time domain and spectral power analyses were used on the results obtained from Holter monitoring. Standard deviation of all R-R intervals (SDNN), standard deviation of the averages of R-R intervals in all 5-min segments of the entire recording (SDANN), SDNN index, the square root of the mean of the sum of the squares of differences between adjacent R-R intervals (RMSSD) and NN50 count divided by the total number of all NN intervals (pNN50) were obtained from the time-domain analyses. Spectral power analysis was used to estimate total power and very low frequency (VLF), low frequency (LF) and high frequency (HF) components. The results from time domain and spectral power analyses were divided into two groups for separately estimating cardiac sympathetic and parasympathetic activities when awake (06:00-22:00h) and asleep (22:00-06:00h). Results are presented as mean +/- SD, a p-value being considered significant if p<0.05. The mean age of the study population was 30 +/- 7 (range: 15-40) years and there were no significant differences between the four groups in terms of gender or age. There was no significant relationship between phase of the moon and CAF (total parasympathetic or total sympathetic activity) but there was a significant positive correlation between brightness of moon and sympathetic activity during the sleep period in women (r=0.224, p=0.028). Even though no relationships between the phase of the moon and CAF was found using HRV analysis, the brightness of the moon affected women's CAF during sleep.