A new nanopesticide, carboxymethyl-bcyclodextrin-Fe 3 O 4 magnetic nanoparticles-Diuron (CM-b-CD-MNPs-Diuron), was synthesized from an inclusion complex of CM-b-CD-MNPs as host and diuron as guest molecules. The transmission electron microscopy revealed it had an average diameter of 25 nm which is more or less the same as that of MNPs (average diameter *23 nm). The CM-b-CD grafting was confirmed by infrared spectroscopy, and the amount of CM-b-CD grafted on the surface of MNPs was determined to be 144.1 mg/g by thermogravimetry. The feasibility of using CM-b-CD-MNPs as a nanocarrier for loading diuron was verified by investigating the formation of inclusion complex. The complexation of CM-b-CD-MNPs with diuron followed the Langmuir adsorption isotherm. In this work, the potential toxic effect of CM-b-CD-MNPs-Diuron on soil microbial was evaluated by microcalorimetry, urease enzyme and real-time quantitative PCR (qPCR). The thermokinetic parameters were observed to decrease with increase in the loading of CM-b-CDMNPs-Diuron in soil. The urease activity data showed that there was a significant effect (p \ 0.05) of CM-b-CD-MNPs-Diuron on the enzyme activity. The microcalorimetric analysis was in agreement with qPCR, confirming the toxic effect of this nanopesticide on microorganism in soil.

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