We have developed a highly tunable film bulk acoustic wave resonator (TFBAR) using magnetostrictive (MS) Fe65Co35 thin films in acoustic layer stack. The resonator acoustic layer stack consists of Pt/ZnO/Fe65Co35 layers to tune the devices. Due toΔ E effect, TFBAR resonance frequency was up-shifted 106.9 MHz (4.91%) in the presence of 2-kOe magnetic field. From experimental measurement, Δ E enhancement was estimated to be 35 GPa. Further, it is observed that return loss (S11), phase response, and quality factor were improved in the presence of magnetic field. This improvement is due to the field-induced stiffness in the magnetic layer. Equivalent-modified Butterworth-Van Dyke (mBVD) circuit model was developed and fit with the experimental data, and circuit parameters were extracted. The proposed resonator is compact, low loss, power efficient, and highly tunable. This method also facilitates a new method of tuning FBAR devices using MS thin films. © 1986-2012 IEEE.