During biologic treatments, attention should be paid to adverse reactions, particularly infectious diseases. Furthermore, drug-induced interstitial lung disease is also known to be associated with biologic therapies. We retrospectively reviewed serum Krebs von den Lungen-6 (KL-6) levels in psoriatic patients who underwent treatment with seven different biologics. A total of 67 patients who received 80 biologic treatments were evaluated. The 31 anti-tumor necrosis factor (TNF)-α treatments consisted of 17 infliximab (IFX) and 14 adalimumab. The 23 anti-interleukin (IL)-23 treatments consisted of 14 ustekinumab and nine guselkumab. The 26 anti-IL-17 treatments consisted of nine secukinumab, six ixekizumab and 11 brodalumab. The IFX showed significantly increased mean serum KL-6 (170.9%), but none of the other treatments showed significant increases. Thirteen of the 17 (75.6%) patients in the IFX and 17 of the 31 (54.8%) patients in the total anti-TNF-α group demonstrated at least a 25% increase in serum KL-6. Levels exceeding the cut-off (500 U/mL) were detected in three patients before treatment and in seven patients after treatment. This study showed that anti-IL-17 and anti-IL-23 treatments have no significant impact on serum KL-6 level. In addition to the influence of IFX, a significantly large number of patients in the IFX group had a history of methotrexate administration associated with psoriatic arthritis, which might have influenced the KL-6 level. None of the patients with elevated serum KL-6 showed pulmonary changes by computed tomography and/or X ray.