The work examined the immune activities among 5 age groups of small abalone (Haliotis diversicolor), i.e., 1 year old to 5 years old. The analyzed immune parameters in this study included total hemocyte count (THC), protein content in plasma, and humoral enzyme activities of acid phosphatase (ACP), alakaline phosphatase (ALP), phenoloxidae (PO), superoxide dimutase (SOD). The results showed that 2 years old abalone had the highest enzyme activities in ACP, ALP, PO and SOD but with lower THC. The 5 years old abalone had the lowest THC, protein content, and enzyme activities of ACP, ALP, and PO. We proposed that the abalone with higher immune activities may resist the stress and pathogen infection more effectively during artificial breeding. In addition, there was a positive relationship between parental immunity and offspring health. Thus, the study suggested that the 2 years old abalone could be a better broodstock among the 5 age groups of abalone.