The present invention provides an aqueous solution composition containing elcatonin as an active ingredient used for hypercalcemia or bone Paget's disease or improvement of pain in osteoporosis, etc. and which is highly stable against shaking, light and heat. This composition contains an effective amount of elcatonin as an active ingredient and a monocarboxy compound and/or its water soluble salt thereof in a molar concentration of 0.05-20 mmol and has a pH of 5.0-6.5 and an ionic strength of .mu.=0.01-0.5. Preferred examples of the monocarboxy compound and its salts are acetic acid, lactic acid, L-histidine, sodium acetate, potassium acetate, sodium lactate, potassium lactate and L-histidine hydrochloride.