Introduction: Anti-tumor necrosis factor α (anti-TNFα) agents can potentially induce the anti-nuclear antibodies (ANA) development over time. Evidence of the real impact of these autoantibodies on clinical response to treatment in rheumatic patients is still scarce. Objectives: To explore the impact of ANA seroconversion induced by anti-TNFα therapy on clinical outcomes in biologic-naïve patients with Rheumatoid arthritis (RA), axial spondylarthritis (axSpA) and psoriatic arthritis (PsA). Methods: An observational retrospective cohort study enrolling biologic-naïve patients with RA, axSpA and PsA who started their first anti-TNFα agent was conducted for 24 months(M). Sociodemographic data, laboratory findings, disease activity and physical function scores were collected at baseline, 12M and 24M. To examine the differences between the groups with and without ANA seroconversion, independent samples t-tests, Mann-Whitney U-tests and chi-square tests were performed. Linear and logistic regression models were used to assess the effects of ANA seroconversion on the clinical response to treatment. Results: A total of 432 patients with RA (N=185), axSpA (N=171) and PsA (N=66) were included. ANA seroconversion rate at 24M was 34.6%, 64.3% and 63.6% for RA, axSpA and PsA, respectively. Regarding sociodemographic and clinical data in RA and PsA patients, no statistically significant differences between groups with and without ANA seroconversion were found. In axSpA patients, ANA seroconversion was more frequent in patients with higher body mass index (p=0.017) and significantly less frequent in patients treated with etanercept (p=0.01). Regarding disease activity, DAS28 for RA patients and ASDAS-CRP for axSpA patients were significantly higher in ANA seroconversion group at 12M (p=0.017 and p=0.009, respectively). For PsA patients, CDAI was significantly higher in ANA seroconversion group at 24M (p=0.043). Overall switching rate of biologic disease-modifying antirheumatic drugs (bDMARD) was significantly higher in the ANA seroconversion group over time (p=0.025). For RA patients, ANA seroconversion predicted DAS28 (β=-0.21, 95%CI[-1.86;-0.18], p=0.017) at 12M.Conclusions: ANA seroconversion induced by anti-TNFα agents could interfere in clinical response of patients with rheumatic diseases. The presence of these autoantibodies can be considered as a potential predictor of poor treatment response and higher need for bDMARD switching over time.