Antimicrobial resistance (AMR) poses a significant global health challenge, impacting humans, animals, and the environment. Dogs and cats are vulnerable to urinary tract infections (UTIs), mostly caused by antimicrobial-resistant Escherichia coli, necessitating antimicrobial susceptibility testing (AST) for optimal treatment. This study investigated and evaluated the seasonality of AST and AMR in urinary E. coli isolates from dogs and cats in the USA and evaluated the potential influence of climatic zones on these patterns. Retrospective data from IDEXX Laboratories, from January 2019 to December 2022, were analyzed. The dataset included 344,862 urinary E. coli isolates (74.2 % from dogs, 25.8 % from cats) tested against seven antimicrobials. Linear regression and negative binomial regression models assessed seasonality and trends, accounting for climatic zone variability. An increasing trend in AST was observed, with a seasonal peak in the summer for both species. Urinary E. coli isolates from dogs and cats had the highest resistance to amoxicillin at 27.9 % (95 % CI: 27.7-28.1) and 28.4 % (95 % CI: 28.1-28.7), respectively, among all antimicrobials tested. Resistance rates significantly declined (p < .01) for all drugs tested in dogs, while in cats, declines were significant only for cefovecin, marbofloxacin, and enrofloxacin. No seasonality in AMR was found at the national level or across climatic zones, though AMR rates varied significantly by climatic zone (p < .01). The hot-humid zone had the highest resistance rates but the lowest AST rates per one million dogs and cats. Seasonality in AST suggests a seasonal pattern for UTIs; however, no seasonal pattern in AMR could be observed nationally or regionally for urinary E. coli isolates.