The aerobic fitness may be defined as the result of a physiologic capacity of the individual to sustain movement over a period of time. The anaerobic ability is the capacity to perform work, which is usually short term in nature, without presence of sufficient oxygen. Present study is concerned with the development pattern of aerobic and anaerobic fitness among preadolescent boys. Total 500 boys were selected randomly from different schools of CoochBehar district for the present study. The range of age of the school boys were from 10 years to 14 years. Cardiovascular endurance and strength endurance were considered to assess aerobic motor ability and running speed and explosive strength were considered to assess anaerobic motor ability. Standard tests were used to measure the performance for all motor abilities. Multiple group design was adopted and five independent groups were formed according to the age of the boys. Total five hundred boys were stratified in equal five age groups and each age group included 100 boys. Mean and SD were used as descriptive statistics and to assess the age trend development of motor abilities ANOVA was used in this study. To find the exact location of difference LSD was used as post hoc test. Result revealed that all aerobic and anaerobic ability increased as the age increases from 10 to 14 years. Peak velocity of development occurred at 11-12 years for CVE and speed but for explosive strength and strength endurance peak velocity of development took place at 12-13 years age for the present subjects.