Toxicity of nano chitosan and fabcomic acaricide were studied under laboratory conditions against adults of spider mite, Tetranychus urticae Koch. Also, LC₅₀ and LC₉₀ of each treatment were determined. The obtained results revealed that fabcomic acaricide was more effective in controlling T. urticae than nano chitosan but it caused pollution for all living organisms as well as to the environment while nano chitosan was more save for both, humans and plants. LC₅₀ for fabcomic acaricide and nano chitosan was 0.1 and 801.04 ppm, respectively. However, LC₉₀ was 1.66 and 5746.09ppm for fabcomic acaricide and nano chitosan, respectively.