It is one of the hot spots in recent years to explore changes in the sleep stage by assessing autonomic nervous activity. In recent years, heart rate asymmetry (HRA) is often used to measure the activity of autonomic nerves. However, the relationship between HRA and sleep stage is not clear. We performed Porta’s index (PI), Guzik’s index (GI), slope index (SI) and area index (AI) analyses on RR intervals per 30-s for understanding the HRA during sleep. Two measurement protocols were set: 1) the HRA values were calculated; 2) the degrees of heart rate deviation from symmetry were estimated. Results showed that PI significantly decreased from N1 and N2 to N3 (p<0.01), and it is increased the highest in REM than other stages (p<0.05). The asymmetry of HRA were significantly lower in N3 (PI and AI p’s<0.05; GI and SI p’s<0.01), and it increased in REM (PI p<0.05; GI, SI and AI p’s<0.0001). The results suggested that HRA has the potential to be used in sleep stage monitoring.