The population of indigenous black rabbits in Viet Nam has been steadily declining, primarily due to the increasing preference for commercial meat rabbit varieties. Consequently, the conservation and systematic breeding of indigenous black rabbits in the Mekong Delta are critical for preserving genetic diversity and sustaining local biodiversity. Sperm conservation is essential for the artificial reproduction of this species. This study aimed to find the optimal concentration of sodium bicarbonate (NaHCO₃) buffer added to Tris Citrate Glucose (TCG) storage medium. Samples after collection were diluted with a storage medium containing sodium bicarbonate at concentrations of 0 mM, 15 mM, 25 mM and 35 mM, then refrigerated at 15ᵒC. The results showed that rabbit sperm achieved the best quality when supplemented with 25 mM NaHCO₃ after 72 hours of storage. Specifically, the sperms had 59.25% overall motility, 22.34% progressive motility, 62.19% viability and 46.77% membrane integrity, the differences were statistically significant when compared with the remaining treatments (p<0.05). The study results indicate that supplementing the TCG preservation medium with 25 mM NaHCO₃ significantly improves the quality of sperm during cold storage. This study has contributed to the development of the sperm conservation medium for indigenous black rabbits in the Mekong Delta.