The effect of melatonin (MT) on the bone tissue (BT) reactive properties was investigated among 80 male Wistar rats at the age of 3, 9, 12 and 16 months. The reactive properties of BT were judged by its ability to polarization under the influence of the alternating electric current. The value of reactance at the frequency of maximum polarization was used as the indicator of BT reactivity. Experimental animals received daily melatonin (Unipharm Inc., USA) at the rate of 1 mg/kg of body mass for 28 days. Freshly isolated femurs of rats served as a material for investigation. Introduction of MT to rats resulted in a significant increase in bone mass and polarization properties of BT. However, the clear tendency to increase the reactance not more than 2.2 % (p < 0.1) compared with the control group among the 3-month old rats were observed, and the increasing the reactance among 9 and 12-month old rats were 6.3% and 12.1% (p < 0.1), respectively. Most significantly, the reactance increased by 21.8% (p < 0.05) among 15-month old animals. Thus the introduction of MT increased the reactivity of BT. This effect had a clear dependence on the age and appeared more among older animals.