In Vietnam, along with unprecedented economic growth, total energy consumption has increased dramatically and doubled over almost last decade. Vietnam industry sector is the largest energy consumer, accounting for 36% of the country total energy consumption. Initial studies show that the potential for energy conservation in the industry sector in Vietnam is about 25% of the current energy consumption level and this potential is untapped. Given that background, our research aims to determine factors influencing energy efficient use in manufacturing firms based in Hanoi. Through employing multiple regression model, analytic results reveal that ownership type, number of unskilled workers in firm, constraint degree of environmental regulations, expenditures for R&D and for machinery and equipment are all related to the energy cost difference between 2004 and 2003, which is considered as a proxy of energy consumption reduction within a firm. The number of unskilled workers and expenditures for machinery and equipment have strongest relationship with the energy cost difference among foresaid factors. Findings of the research imply that firms should give more attention to training available workers and diversifying capital sources for promoting investments in machinery and equipment.