This dataset contains nifH gene copy numbers, growth rates, and grazing mortality rates of endosymbiotic nitrogen-fixing cyanobacteria (i.e., UCYN-A1 and UCYN-A2/3/4) in the western Bering Sea. The associated physicochemical factors including temperature, salinity, iron, nitrate+nitrite, ammonium, phosphate, silicate, and chlorophyll a are also available in this dataset. All these data were collected during a research cruise to the western Bering Sea on R/V Professor Multanovskiy from July to August 2018.  In addition, the growth rate and grazing mortality rate of total phytoplankton community (inferred by chlorophyll a), which are belonged to a larger dataset reported by Liu et al., (in review), are used for comparing with the rates of UCYN-A in this study. Liu, K. and others (under review) Phytoplankton and microzooplankton population dynamics along the western area from the North Pacific to the Bering Sea in summer.