We have successfully prepared three dimensional carbon nanotube foams (CNTF) by a simple environmental-friendly method. However, the as-grown CNTF shows a high electrical conductivity but a reduced specific surface area which limits its application as electrode materials in energy storage devices. In this work, the as-grown CNTF has been activated by using certain concentration of KOH aqueous solution. The results indicate that activation can enlarge the specific surface area by producing new pores with sizes from micropore to macropore, but give no important change in shape and size of the CNTF. We take the activated CNTFs as electrodes for supercapacitors and lithium-ion batteries respectively, and find that activation can clearly enhance the specific capacities and rate properties due to the enhanced specific surface area and hierarchical porous structures. The activated three dimensional CNTF materials can also be used as supporters for other active materials indicating a potential application prospects.