Background: Psoriasis is a chronic immune-mediated inflammatory disease. Ustekinumab is an effective biological treatments in plaque psoriasis. However, there have been few studies on patients with plaque psoriasis who did not show clinical improvement after the administration of ustekinumab. Objectives: To evaluate the changes in psoriasis area severity index (PASI) through a year follow-up and to analyze the demographic characteristics of the patients with plaque psoriasis who did not achieve PASI 75 at 16 weeks after ustekinumab use. Methods: We reviewed the medical records and clinical photographs of 20 patients with plaque psoriasis who were treated with ustekinumab and did not achieve PASI 75 on the 16 weeks assessment. The PASI scores were evaluated at 16 and 48 weeks, and demographic characteristics were investigated. Results: There were 10 patients in each group, and after 48 weeks, the PASI change and the average age was 88.15±4.35 %, 42.3±12.05 years old and 65.03±8.86 %, 54.4±12.62 years old (p<0.05), In addition, there were no statistically significant differences between the two groups in terms of sex, disease duration, BMI, smoking, drinking, family history, arthritis, nail involvement, and comorbidities. Conclusion: Among the patients who showed persistent lesions even after ustekinumab treatment, patients in the group with a large PASI change were younger than those in the group with small PASI change, at 48 weeks. Other factors have no association.