Biomolecular condensates are micrometer-scale subcellular structures assembled through protein phase separation in living cells. Recent research shows that they are critical to normal biological processes and their misregulation may contribute to disease. A prominent example is the cancer-causing EML4-ALK fusion protein, which spontaneously forms biomolecular condensates that significantly enhance receptor tyrosine kinase (RTK) signaling within the condensate microenvironment. In this work, we show that a trimerization domain (TD) in EML4-ALK is necessary for condensate formation. By designing a peptide targeting the TD, we disrupted EML4-ALK self-assembly, leading to the dissolution of pre-existing EML4-ALK condensates in patient lung tumor-derived cells. Notably, this disruption significantly reduced EML4-ALK-dependent signaling and cell proliferation. Our findings demonstrate that interfering with a specific protein-protein interaction can disrupt oncogenic biomolecular condensates and attenuate their associated signaling. These results highlight the potential of targeting condensate assembly as a strategy to modulate oncogenic signaling.