We experimentally demonstrate high quality factor spin wave resonances in an encapsulated thin film of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x∼2) coated on an a-plane sapphire substrate by low temperature chemical vapor deposition. The thickness standing wave modes are observed in a broad frequency range (1 GHz–5 GHz) with high quality factor exceeding 3200 in ambient air at room temperature, rivaling those of inorganic magnetic materials. The exchange constant of V[TCNE]x∼2, a crucial material parameter for future study and device design of the V[TCNE]x∼2, is extracted from the measurement with a value of (4.61±0.35)×10−16 m2. Our result establishes the feasibility of using organic-based materials for building hybrid magnonic devices and circuits.