The present invention relates to a pharmaceutical composition for preventing or treating inflammatory disease, colorectal cancer and prostate cancer, which contains an A3 adenosine receptor agonist, 2-chloro-N6-(3-iodobenzyl)-4′-thioadenosine-5′-N-methyluronamide (thio-Cl-IB-MECA), N6-(3-iodobenzyl)-4′-thioadenosine-5′-N-methyluronamide (thio-IB-MECA), or a pharmaceutically acceptable salt thereof. The pharmaceutical composition of the invention is significantly less toxic than conventional A3 adenosine agonists, and thus is useful for prevention or treatment of inflammatory disease. In addition, it more selectively inhibits the growth of androgen receptor-dependent or independent prostate cancer cells than other A3 adenosine receptor agonists and thus is useful for prevention or treatment of colorectal cancer or prostate cancer.