The major forces of technological change and input substitution induced by relative factor price changes have led to important changes in the input mix in Bangladesh agriculture.  The labour input has been replaced by fertiliser and irrigation. This change in input use raises significant issues with respect to the nature of factor substitution and input demand. This study sheds light on these issues by using the translog cost function approach. The findings reveal that the AES between land and fertiliser (N-F) shows increasing substitutability relationship over time, whereas the AES between fertiliser and irrigation (F-I) displays high substitutability throughout the study period along with a declining trend in the latter period.