The development of selective and efficient catalysts is essential if practical application of CO2 electroreduction is to be realised. The C1 products CO and formate are two of the economically viable products generated from this technique. In this work, we report an aligned copper oxide derived nanowires catalyst with tunable selectivity for producing CO or formate in aqueous media. The catalyst with nanowires less than 2.3 ��m converts CO2 to CO with a high CO/formate ratio of 2.52, while formate is the dominant product on longer nanowires (��� 2.7 ��m) with a low CO/formate ratio of 0.63. Good selectivity of 63% for CO and 52% for formate are achieved on 2.3 ��m and 2.7 ��m nanowire catalysts respectively at a modest overpotential of 690 mV. The length dependent product selectivity is correlated to the surface structure and local pH environment which may affect the formation of intermediates and the pathways towards products. This work highlights how product selectivity is dependent on the length of Cu NWs used during the CO2 electroreduction.