This research investigates the seismic performance of pile foundations reinforced with micropiles, with a particular focus on the intricate dynamics of nonlinear soil-structure interactions under strong ground motions. General seismic retrofitting strategies often prioritize structural components above the soil surface, overlooking the potential ramifications of underlying soil behavior and its interaction with the foundation. Micropiles, characterized by their high-strength properties, present a promising solution for retrofitting existing pile foundations. However, their performance is intricately tied to the dynamic interaction with the surrounding soil. To assess the seismic performance of pile foundations retrofitted with micropiles, this current study utilizes scaled-model testing on a micropiles-reinforced 2 × 2 pile group under 1 g conditions. The study examines the dynamic relationship between micropiles and soil, taking into the consideration of nonlinear soil-pile and pile-to-pile interactions. Additionally, effects of micropiles inclination on the overall seismic performance is also assessed. The outcomes of this research offer some valuable insights into the efficacy and reliability of micropiles as retrofitting elements under seismic loadings. Furthermore, it also underscores the importance of the effects of nonlinear soil-structure interactions in the development and evaluation of foundation retrofitting strategies.