An Fe$_{49}$ Co$_{49}$ V$_2$alloy is annealed in thermal annealing furnace at 50$0^{circ}C$, 75$0^{circ}C$, 80$0^{circ}C$, and 90$0^{circ}C$. Annealed samples were cooled in air. The magnetostriction is measured by using a Michelson laser interferometer. Receiving the feedback signal of interference, a mirror attached to piezoelectric transducer (PZT) maintains the optical path length (OPL) between two arms of laser interferometer relatively constant. The feedback voltage is calibrated to the OPL variation. A magnetostriction of 2$ imes$10$^{-6}$ at H = 60 Oe increases up to 33.68$ imes$10$^{-6}$ at an annealing temperature of 90$0^{circ}C$, suggesting that the magnetostrictive characteristics are improved by the microstructural modification.