A 30-day study was conducted on the effects of diets supplementation with 0, 1.0%, 3.0%, and 5.0% Sonneratia alba leaf extracts on healthy goldfish, Carassius auratus against Aphanomyces invadans. Results showed that the numbers of white blood cell significantly increased in the infected fish fed with 3.0% and 5.0% supplementation diets after the second week of experiments. Whilst the numbers of red blood cell significantly decreased in the infected fish fed with 0 and 1.0% supplementation diets. After the third week of feeding trials, the total protein, albumin level and lysozyme activity were significantly increased in the infected fish fed with 3.0% and 5.0% supplementation diets. However, the myeloperoxidase activity significantly increased after two weeks in the infected fish were fed with 3.0% and 5.0% supplementation diets. The cumulative mortality rate of goldfish decreased up to 17% when the infected fish were fed with 3.0% supplementation diets. This study indicates that enriched fish feed with 3.0% and 5.0% S. alba leaf extracts enhanced the non-specific immunity and survival rate of the goldfish, suggesting that the extract may serve as a potential prophylactic treatment against A. invadans.