The basic foundation behind cryptography as a discipline was to research how valuable data, information can be protected from unauthorized parties, such as adversaries. Quantum cryptography is one of the recent advancement occurred within that discipline. However, this cryptographic algorithm still at its early stages, where there is no wide implementation can be seen. Many research papers have been done to develop this algorithm, while others, to propose new implementations of this algorithm to tackle a specific problem. This research paper studies and examines the relationship between the QKDS (Quantum Key Distribution System) and the parity bits. Hence, explore how the use of parity bits can improve the final resolved key.