The complex formation and a liquid-liquid extraction in the cobalt (II) - 4-Nitro-2-hydroxythiophenol (HNTP) - diphenylguanidine (DPG) - water - chloroform system was studied. The optimum extraction-spectrophotometric conditions were found. The molar ratio of the reacting species was determined to be 1:2:2 (Co: HNTP: DPG). The following equilibrium processes were quantitatively examined: the association between the anionic chelate, [Co²⁺(HNTP)₂]^2–, and the diphenylguanidine (lgβ =4.8); the distribution of the ternary complex be­tween the aqueous and organic phases (lg K_D=0.88); and the extraction from water to chloroform (lgK_ex=lgβ +lgK_D=5.6). The effect of foreign ions and reagents on the extraction was studied. A sensitive (ε₅₆₀=4.3×10⁴ L mol^–1 cm^–1) and simple extraction-spectrophotometric procedure for cobalt determination was developed.