In this paper, we propose an adaptive capacity allocation scheme at the call level for a blocked call cleared loss system. The scheme aims to maintain the connection blocking probability around a specified target value by dynamically adjusting the allocated capacity. Based on a fluid flow model of the loss system, Lyapunov Stability theory is used to derive an adaptive capacity adjustment scheme which guarantees overall system stability around the target call blocking probability. Numerical results are given which show that the Lyapunov control based scheme is robust to load variations and performs better than existing schemes in the literature.