The magnitude of changes in average crop production and the sources of changes were measured for six crops- Aus rice, Aman rice, Boro rice , jute, wheat and sugarcane between two time periods pre-modern technology adoption period and modern technology (MT) adoption period. Except for wheat, these periods were defined as 1947/48 -1967/68 and 1968/69- 1986/87 respectively. For wheat, these periods were defined as 1947/48-1971/72 and 1972/73 -1986/87 respectively. The analysis shows that production, area and yield increased at the national level for all the crops except jute. Although area under jute increased, its production and yield declined in the second period. Change in mean area was the main source of mean production change in sugarcane, Aus rice and Boro rice. But yield was the main source of increase in Aman rice production and decrease in jute production. For wheat, interaction between changes in mean area and mean yield was the principal source of change in production. And yield of all these crops except jute increased due to the adoption of modern technology (MT). Finally, some policy conclusions are drawn with respect to an improvement of production levels of the major crops.