Psoriasis is a chronic, inflammatory skin disease in which the interleukin (IL)-23/IL-17 axis plays a central role. Bimekizumab is a novel antibody that targets both IL-17A and IL-17F. This retrospective study aimed to assess the long-term effectiveness and safety of 52-week treatment with bimekizumab, and to identify predictive factors for short- (16 weeks) and long-term (52 weeks) responders (i.e., achievers of a Psoriasis Area and Severity Index (PASI) score of 100) to bimekizumab in Japanese patients with psoriasis. The study was conducted on 56 Japanese patients (aged ≥ 15 years) with moderate-to-severe psoriasis treated with bimekizumab from May 2022 to March 2024. The therapeutic effectiveness was evaluated by the transition of PASI scores during treatment. Baseline characteristics and clinical and laboratory indexes were compared between responders and poor responders. Treatment-emergent adverse events (TEAEs) were recorded to assess the safety of the treatment. At week 52, the achievement of PASI 100, static Physician's Global Assessment 0/1, and the Dermatology Life Quality Index 0/1 were 72.4%, 94.7%, and 93.3%, respectively. Short-term responders showed lower baseline values of neutrophil-to-lymphocyte ratio, monocyte-to-lymphocyte ratio (MLR), and systemic inflammatory response index compared to poor responders. Long-term responders showed younger age and lower MLR compared to poor responders. TEAEs were mild or moderate, without serious adverse events. Long-term treatment with bimekizumab is effective and safe for psoriasis patients. Lower MLR and younger age might predict long-term response to treatment with bimekizumab, aiding in personalized treatment strategies.