Due to concerns about the sustainability of the energy sector, conversion of biomass to energy is increasing its hold globally. Life Cycle Impact Assessment (LCIA) is being adopted as an analytical tool to assess the environmental impacts in the entire cycle of biomass production and conversions to different products. This study deals with the LCIA of straw conversion to district heat in a Combined Heat and Power (CHP) plant and in a district heating boiler (producing heat only). Environmental impact categories are Global Warming Potential (GWP), Acidification Potential (AP), aquatic and terrestrial Eutrophication Potential (EP) and Non-Renewable Energy (NRE) use. In the case of CHP, the co-produced electricity is assumed to displace the marginal Danish electricity mix. The current study showed that straw fired in the CHP plant would lead to a GWP of -187 g CO2-eq, AP 0.01 m(2) UES (un-protected ecosystem), aquatic EP 0.16 g NO3-eq, terrestrial EP 0.008 m(2) UES, and NRE use -0.14 MJ-primary per 1 MJ heat production. Straw conversion to heat in the CHP plant showed better environmental performances compared to the district heating boiler. Furthermore, removing straw from the field is related to the consequence e.g. decline in soil carbon sequestration, limiting soil nutrient availability, and when compared with natural gas the conversion of straw to heat would lead to a higher aquatic and terrestrial EP and AP. The study also outlays spaces for the detail sustainability assessment of straw conversion in a biorefinery and compare with the current study. (C) 2014 Elsevier Ltd. All rights reserved.