Fine roots are known to be the fundamental contributors to soil carbon (C) in boreal zone and root-derived C is more refractory as compared to those from the aboveground litter. Root phenology as a driver of belowground C allocation is poorly understood especially in deciduous (i.e. Larch dominated) boreal forests. Seasonal dynamic of root biomass in fire-affected boreal forests received rather little scientific attention. We investigated seasonal dynamics of fine root biomass and necromass for dominant tree species (Larix gmelinii, Betula platyphylla) and understorey vegetation in control and burnt stands. Fine roots total mass did not differ statistically between stands despite a profound difference in aboveground biomass (control stand is 8 times higher). Maximum of total fine root mass occurred in September and was 599 g m^-2 and 695 g m^-2 in control and burned sites respectively. In background forest tree fine roots comprise about 60% of root biomass but in burned site understorey vegetation is the major contributor to root biomass. Our results show that forest fire could alter the structure of fine root biomass affecting both the quantity and quality of soil organic matter. These findings help us to predict how boreal ecosystems may respond to future climate change.