A population of Cassiopea andromeda was observed in the Nayband Bay, nearby Assaluyeh, from Bushehr province- Iran, in spring 2014. It was the first record of this invasive species in Iran. The enormous Swarming was commonly located at depths of 0.5–3 m, on muddy–sand bottom in declared lagoon in Northwest of the Persian Gulf. These aggregations were including about 4-5 cases in every one m2, different in size, typically between 6–15 cm in diameter. The venomous jellyfish C. andromeda can cause envenomation with their nematocysts and occurrence of certain signs like pains, swellings, rashes, itching, vomiting and other toxicological effects, depending on sensitivity of the victims to the venom.