Ran Chen, Wenbo Li, Wenhua Jiang, Bangyou Zheng, and Jinhua Li (2018) Mother-offspring interactions are widespread in humans and other mammals, and play an important role in offspring survival and development. Mother-calf interactions have been described in a wide range of ocean cetacean species, but they have not yet been documented in freshwater cetaceans. In this study, we observed the behavior of two mother- calf pairs of Yangtze finless porpoises living in Tongling Freshwater Porpoise National Natural Reserve, China, to explore the maternal relationship between mother porpoises and newborn calves during the calves' first year. The results showed that mothers performed significantly more approach behaviors and fewer leave behaviors than calves during the lactation period, but performed significantly fewer approach and more leave behaviors than calves during the non-lactation period (starting from the seventh month after birth). The landmarks for maintaining intimate relationships within each mother-calf pair occurred within sixth months of birth. The duration of calf separations from their mothers increased with calf age.