A new tintinnid ciliate, Tintinnopis estuariensis sp. nov. was found in the estuary of Yangtze River, China. It was most abundant in September. Its arenaceous lorica is cylindro-conical in shape, (120–180) μm × (50–75) μm in size, agglutinated with mineral particles, and open at both ends. Two characters distinguish it from others: the unique lateral flattened posterior portion with a vertical aboral opening and wider oral diameter. It occurred in water with surface temperature of 14–27°C and surface salinity of 3.9‰–29.8‰.