Purpose: The purpose of this study was to investigate the effects of the information providing program of $I^{131}$ treatment on the pre-treatment anxiety and immune response of patients with thyroid cancer. Method: The used design was a nonequivalent control group design with pretest and post-test. Subjects of this study were 54 patients who had received a total thyroidectomy. They were given a information providing program with a brochure before 4 weeks of the hospitalization for $I^{131}treatment$, with problem solving phone counseling before 2 weeks of the hospitalization. Collected data were analyzed using the SPSS WIN program. Result: Hypothesis one, "The anxiety score of an experimental group would be lower than the score of a control group" was supported(t = -2.12, p = .03). Hypothesis two, "The level of cortisol of an experimental group would be lower than the level of a control group" was supported(t = -3.19, p = .00). However, hypothesis three "The level of T, B and N-K cells of an experimental group would be higher than the level of a control group" was not supported. Conclusion: The information providing program of $I^{131}$ treatment effectively decreased the anxiety of patients with thyroid cancer.