Objective: This study aims to determine the trace cadmium in water and fish species from estuaries in Tien Hai, Thai Binh province, Vietnam by graphite furnace atomic absorption spectrometry (GF-AAS). Methodology: The optimal conditions has been investigated by studying the effects of analysis parameters such as spectral line, current of cathode lamp, slit width, furnace temperature, acid concentration and subtracted solution on absorbance. The validation method was evaluated by linear range, accuracy, repeatability, limit of detection (LOD), limit of quantitation (LOQ), recovery (Re), and determination of trace cadmium in water and fish species. Findings: The results showed that the spectral line of 228.3 nm, current of cathode lamp of 4 mA, slit width of 0.5 nm, furnace temperature of 1800 ◦C, HNO3 concentration of 1%, CH3COONH4 concentration of 1% were optimal conditions for determination of cadmium. At these conditions, the analytical procedure exhibited the high accuracy and repeatability. The linear range of cadmium was 0-4 ppb. The LOD and LOQ values were 0.0058 and 0.019 ppb, respectively. Application/Improvements: Determination of the trace cadmium in the water and fish samples was done by the development of analytical procedure. It was applied to determine the water and fish species from Ba Lat and Lan estuaries in Tien Hai, Thai Binh, Vietnam. Keywords: GF-AAS; Trace; Cadmium; Analysis; Fish