Objective: To investigate the effects of powdered silver zeolite (SZ) on the in vitro fish pathogen Saprolegnia sp. growth of the Methods: The antifungal activity of SZ was evaluated by determining the minimum inhibitory concentrations using two-fold serial dilutions of powdered SZ in a glucose yeast extract agar at 22 °C. The growth of Saprolegnia sp. on the SZ agar treatments was compared to that on SZ-free agar controls. Results: The results showed that SZ had an inhibitory effect on the in vitro growth of the tested mfugn/gLi,. wThheic mh iins iemquumal itnoh 0i.b0i6t opreyr cceonntc.entration of SZ for Saprolegnia sp. was also calculated at 600 Conclusions: SZ is a potential good candidate to replace teratogenic and toxic agents, such as malachite green in aquaculture systems.