Abstract the objective of this research was to determine the effect and the optimum concentration of avicennia marinaleaf extract on prevalence, hatching rate and hatching time of goldfish eggs that were infected by saprolegnia sp. the research was conducted at balaibenihikan (bbi) lukupbadak, aceh tengah district on june 2016. the completely randomized design method was used as statistical analysis method in this study with five treatments and 4 replications. samples were the fertilized goldfish eggs that were infected by saprolegnia sp. then treated by immersing in the extract. the treatments were the different concentrations of extract, namely; 0, 5, 10, 15 and 20 ppm. the result of anova showed that the extract gave the significant effect on the prevalence, hatching rate and hatching time of goldfish eggs (p