We investigated the abundance and biomass of planktonic ciliates in the sea around Zhangzi Island, Northern Yellow Sea, in July and August 2010. Ciliates were sampled from surface, middle and bottom depths at nineteen sample stations along three transects (Transect STA, Y1 and Y2). A 1-L water sample was collected at each depth with a 2.5-L Niskin water sampler and fixed in 1% acid Lugol's iodine solution. The bottles were stored in the dark for up to two months until analyzed. The fixed water samples were left to settle for at least 48 h in plastic bottles and the supernatant was siphoned out until a 150 mL sample was left. The concentrated sample was examined and counted following the Utermöhl method. A subsample of 16 mL of the concentrated sample was settled in Utermöhl sedimentation chambers and counted using an Olympus IX51 inverted microscope at 100× or 400×. The classification of tintinnids was based on taxonomic literature. The dimensions of the ciliates were measured and the cell volume of each species was estimated using appropriate geometric shapes. Non-loricate ciliates were divided into three size classes by cell volume: NCI (10³ to 10⁴ μm³), NCII (10⁴ to 10⁵ μm³) and NCIII (>10⁵ μm³). The carbon-to-volume ratio used to calculate biomass was 0.19 pg C/μm³. The plasma of tintinnids was assumed to occupy 30% of the lorica volume. Abundance and biomass of the ciliates cross-water column were calculated as the integral of the abundance and biomass from the bottom to the surface. The results showed that the average abundance of total ciliates in July and August was (5107±4451) ind/L and (7894±7212) ind/L, respectively. The average biomass of total ciliates was (10.17±9.06) μg C/L and (15.24±18.49) μg C/L. Surface ciliate abundance and biomass decreased from coastal to offshore waters in July. Surface ciliate abundance was higher at St. Y1-3 and St. Y2-5 while surface ciliate biomass was higher at St. Y2-5 and St. Y1-1. Ciliate abundance decreased from the surface or subsurface down to the bottom along Transect STA in July, Transect STA and Y1 in August, while it was vertically homogeneous along Transect Y2 in August. The average abundance and biomass of total ciliates cross-water column were higher in coastal waters than in offshore waters in July and were higher at St. Y2-5 and St. Y1-1 in August. A total of 17 and 21 tintinnid species were identified, in July and August respectively. Nearly 50% of species were in the genus Tintinnopsis, and we recorded the species Tintinnopsis corniger Hada, 1964 for the first time in Chinese waters. Tintinnids occupied (19.0±21.6)% and (13.0±16.1)% of the total ciliate abundance and (58.2±33.0)% and (42.6±33.2)% of the total biomass in July and August, respectively. Small bio-volume ciliates dominated in total non-loricate ciliate abundance in both July and August.