Structures of CnAs- (n = 1-11) clusters have been determined by means of B3LYP density functional method. A comparison of structure stability shows that the lowest-lying structures are linear, with the arsenic atom located at one end of the carbon chain. Also, the linear CnAs- (n = 1-11) anions with an odd number of carbon atoms are more stable than those with an even number, in good agreement with the peak pattern of time-of-flight investigation. The trend of such odd/even alternation is explained on the basis of concepts of electronic configurations, incremental binding energies, vertical electron detachment energies, and dissociation channels.