Electrochemical lithium insertion have been carried out in different compositions within the solid solution Nb8-xW9+xO47 (1 less than or equal to x less than or equal to 6). Through galvanostatic and potentiostatic techniques, we have detected that lithium insertion proceeds by at least two reduction steps. These processes seem to be related to the molar ratio Nb/W. The maximum lithium content reached during the discharge process leads to a specific capacity of 170 Ah/kg. Nevertheless, due to irreversible structural transformations in the matrix-host, such capacity is lost after the first cycle. A detailed analysis about the insertion kinetic process will be discussed in this work. (C) 2003 Elsevier Science Ltd. All rights reserved.