Multipath Transmission Control Protocol (MPTCP) aims at the proper utilization of the available bandwidth of multiple paths. Big widow size of congestion control algorithm ensures more data delivery. Therefore, many recent researches have focused on the congestion window increase mechanism to quickly reach to an optimal value. In case of loss events, they halve the congestion window following traditional TCP. However, this causes the congestion window to wait longer to reach an optimal state wasting network resource. In this work, a dynamic congestion window decrease mechanism is presented that determines the decrease factor based on previous congestion state and current congestion state. We have evaluated our scheme in network simulator NS-3. The results show that the proposed scheme highly enhances the total throughput and path utilization.