In this work, chitosan dithiocarbamate (CSDTC) derivative was successfully synthesized by mixing chi-tosan with carbon disulfide and ammonia at 45^oC. Then, CSDTC (40  μL, 1.0 mg/mL) was added into AuNPs solution to obtain the chitosan dithiocarbamate functionalized gold nanoparticles (CSDTC-Au NPs).The Cd²⁺ ion was quickly induced the aggregation of CSDTC-Au NPs at PBS pH 8.0, which facilitates todevelop a simple and selective colorimetric method for detection of Cd²⁺ ion. As a result, the characteristicsurface plasmon resonance (SPR) peak of CSDTC-Au NPs at 523 nm was red-shifted to 685 nm, yielding a color change from red to blue. Under the optimized conditions, a linear relationship (R²= 0.9991) was observed between the absorbance ratio at A_685nm/A_523nm and the concentration of Cd²⁺ in the range of 50–500  μM. The limit of detection was found to be 63 nM. Furthermore, CSDTC-Au NPs was applied todetermine Cd²⁺ ion in water sample