This study reports on deoxyribonucleic acid (DNA) immobilization in a microcapsule and the adsorption of toxic substances. Salmon testes DNA was immobilized using a microencapsulation method and the immobilization efficiency of DNA, stability of microcapsulated DNA and adsorption properties of toxic substances were investigated under various experimental conditions. This study succeeded in immobilizing over 90% of DNA in the DNA dosage based on the thymine base and the microcapsulation of DNA showed high reproducibility for immobilization efficiency. Immobilized DNA in the microcapsules did not leak, regardless of the salt concentration and pH values in the external aqueous phase. Microcapsulated DNA could selectively adsorb toxic substances that have a planar structure. Based on these results, it was shown that the microcapsulated DNA is a good adsorbent for toxic substances and the microcapsulation method is useful for immobilizing DNA in a polymer matrix.