OBJECTIVE: To study the chaotic characteristics and power spectrum characteristics of heart period signals (HPS) in children with asthma. METHODS: The parameters of the chaotic characteristics and the power spectrum characteristics of HPS were detected using a computerized system for analyzing chaotic characteristics of HPS in 47 children with asthma and 103 normal children. These parameters were tested in the remission phase in 18 of the 47 asthmatic children to analyze their changes.RESULTS: Of the parameters of the chaotic characteristics, relative dispersion of heart period (HRD), lyapunov exponent of heart period (HLE) and heart cycle chaosness (HCC) ( 4.50 ± 2.06 , 3.17 ± 1.26 and 26.34 ± 13.78 , respectively) in the children with asthma were all lower than those in the normal children ( 7.29 ± 1.62 , 5.09 ± 0.99 and 51.08 ± 17.32 , respectively)(P< 0.01 or 0.05 ). Of the parameters of the power spectrum, the power value in very low frequency band (PVV), power value in low frequency band (PVL), power value in high frequency band (PVH), power rate in very low frequency band (PRV), power rate in low frequency band (PRL), power rate in high frequency band (PRH), ratio of power in very low frequency band to that in high frequency band (RVH), ratio of power in low frequency band to that in high frequency band RLH and total frequency band power (TFP)[( 320.61 ± 372.28 ) ms 2, ( 221.00 ± 243.86 )ms 2, ( 224.38 ± 327.51 )ms 2, ( 42.84 ± 18.47 )%, ( 26.58 ± 17.63 )%, ( 2.72 ± 2.74 ), ( 1.79 ± 1.58 ), and ( 827.44 ± 933.22 ) ms 2, respectively] differed from those in the normal children (P< 0.01 or 0.05 ). These abnormal parameters of asthmatic children got recovery with different degrees in the remission phase. CONCLUSIONS: The complexity of the heart state is reduced in children with asthma, and the control ability of the autonomic nervous system for the heart is also depressed. The functional disorder of autonomic nerves of asthmatic children in the attack phase might be temporary and reversible.