In order to discuss the property of selenium as a ligand atom and the effect of the substituent to complex formation in the related compounds of selenocysteamine, y-aminopropylselenol, ot-dimethyl-fl-aminoethy selenol, a-methyl-i3-aminoethylselenol, N-ethylaminoethylselenol and N,N'-dimethylaminoethylselenol were synthesized. Acid dissociation constants were determined by potentiometric titration and the values were compared with those of sulfur analogues. Stability constants of their metal complexes were calculated.