We investigated the adsorption of C2H radical on small cobalt clusters by mass spectrometry and by measuring the photoelectron spectra of ConC2H- (n = 1-5) cluster anions. The most stable structures of ConC2H-(n = 1-5) and their neutrals were determined by comparing the experimental results with theoretical calculations. Our studies show that C2H radical still maintains its integrity as a structural unit in ConC2H- clusters, rather than being divided by Co-n clusters. The most stable isomers of Co1-2C2H- clusters are linear with the C2H interacting with only one Co atom, while those of Co3-5C2H- cluster anions are quasi-planar structures with the carbon-carbon bonds bending slightly toward the Co3-5 clusters. The carbon carbon bond of C2H is lengthened more in Co3-5C2H- clusters than in Co1-2C2H-.