Regular physical exercise causes resting bradycardia. This exercise-induced resting bradycardia may be associated with exercise-induced changes in Cardiac autonomic nervous activities (CANA). Power Spectral Analysis (PSA) of Heart rate variability (HRV) is one of the most promising new techniques to quantify CANA. Regular physical exercise induced bradycardia is associated with exercise-induced adaptation in CANA. To observe the HRV parameters by frequency domain method (PSA), in male adolescent athletes in order to find out the influence of regular physical exercise on resting heart rate (HR) and CANA. The cross sectional study was carried out on 62 adolescent male athletes aged 12-18 years (group B), in the Department of Physiology, Bangabandhu Sheikh Mujib Medical University from 1st July 2007 to 30th June 2008. For comparison 30 age, sex and socioeconomic condition matched apparently healthy sedentary subjects (group A) were also studied. The study group was selected from the BKSP (Bangladesh Krira Shikka Prothistan, Savar, Dhaka) and the control from a residential school of Dhaka city. HRV parameters were assessed by Polygraph (Polyrite D, version 2.2). For statistical analysis Independent-Samples t-test was done as applicable. Resting mean HR was significantly (p<0.001) lower in the athletes. The mean value of Total (variance), VLF, LF and HF power was significantly (p<0.001) higher in athletes than that of non-athetes. Regular physical exercise-induced resting bradycardia is associated with exercise-induced adaptation in cardiac autonomic nervous activities.