The complexation of water soluble dinitrosoresorcinol (DNR) with Co+2 was studied spectrophotometrically. A new sensitive and selective spectrophotometric method for the determination of Co+2 with DNR was developed. The Co+2-DNR complex was formed quantitatively in the pH range 5.0-9.0 with an absorption maximum at 397 nm. The DNR reacts with Co+2 to form 1:3 stable (metal : ligand) complex. The Beer law was obeyed over the range of 1 x 10(-2)6x10(-1) mg L-1 and molar absorption coefficient (epsilon) of Co+2-DNR complex was 3.64 x 10(4) L mol(-1) cm(-1) at 397 nm. The interference of cations and anions was also investigated and especially the interference of Ni+2, Cu+2, Fe+3 were eliminated by the use of EDTA. The relative standard deviation of this method was found to be 5%. The developed method was applied to the determination of cobalt in standard Euronorm-CRM 585-1 Ferro-Chromium and Analysen-Kontrollprobe 530-1 samples. The obtained results of the analysis were very close to those of those stated for the standards.