Different kinds of Al and Al alloys are used for all bare overhead energy transmission lines. In the present work, the effect of heat treatments on the conductivity of Al-0.25wt.%Zr alloy has been investigated. Al-0.25wt.%Zr samples were prepared in cold graphite crucibles by using a vacuum furnace and a continuous casting line. The samples were aged isothermally and isochronally in muffle and tube furnaces. Aging was carried out at a wide range of temperatures (350-600 degrees C) at constant aging times (75 h, 100 h) and a wide range of aging times (25-500 h) at constant temperatures (425 degrees C, 450 degrees C). According to the experimental results, conductivities of aged samples increase up to a certain aging temperature and aging time and reach peak values, then decrease with increasing aging temperature and aging time.