Optical packet switching (OPS) is expected to realize low latency communication and low power consumption by eliminating the optical-electrical-optical (OEO) conversion in the switching process. However, due to the unavailability of practical optical buffer in OPS, nonnegligible packet loss may occur even under low loads. Since all kinds of existing TCP are not designed to adapt to such a bufferless environment, various problems may occur when conventional TCP is used in OPS networks. In this paper, we evaluate the performance of using conventional TCP in bufferless OPS networks through network simulation. As a result of our study, we found that there is serious degradation problem in network throughput and fairness, mainly caused by the vulnerability in establishing TCP connections and frequent retransmission timeout (RTO) occurrence.