The invention discloses a fish drug for treating oodiniosis. The fish drug is prepared from the following raw materials in parts by weight: 10-20 parts of coptis chinensis, 5-10 parts of honeysuckle, 20-30 parts of polygonum perfoliatum, 5-10 parts of sanguisorba officinalis, 10-20 parts of radix isatidis, 1-5 parts of subprostrate sophora, 30-40 parts of amomum tsao-ko and 1-5 parts of common carpesium fruit. The fish drug for treating oodiniosis disclosed by the invention is good in treatment effect, hardly causes side effects and does not pollute a fish pond.