Accumulating evidence has suggested that the tumor micro-environment of nonsmall-cell lung cancer (NSCLC) may be impacted by chemotherapy, radiotherapy, or epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). PD-L1 is an important biomarker in the tumor microenvironment that can predict patient response to immunotherapies. Therefore, it is highly desirable to achieve a real-time, noninvasive assessment of PD-L1 expression, which can provide critical information for recruiting patients as well as monitoring therapeutic efficacy. We herein studied the EGFR-TKI-induced effects on PD-L1 levels in NSCLC tumor models using immuno-PET imaging with Zr-89-Df-KN035, an imaging tracer previously established by our group. A549 human NSCLC xenografts were established in BALB/c nude mice and treated with different doses of an EGFR-TKI gefitinib. PET imaging with Zr-89-Df-KN035 was performed before and after the treatment to evaluate PD-L1 expression, which was further verified by immunohistochemical staining. Our results demonstrate that Zr-89-Df-KN035 can specifically evaluate PD-L1 levels in NSCLC tumor models. Compared to the untreated control, the high dose of gefitinib inhibited tumor growth and lowered the tumor uptake of Zr-89-Df-KN035. In comparison, the low dose of gefitinib did not affect tumor growth, although the extensive tumor necrosis also led to the lower uptake of Zr-89-Df-KN035. In conclusion, our results demonstrate that immuno-PET imaging with Zr-89-Df-KN035 is a promising tool to noninvasively monitor PD-L1 expression in NSCLC treated with EGFR-TKIs and can be used to optimize treatment plans for immunotherapy.