(Presented on ; published online )A hybrid thin-film coplanar-line with a slit-patterned CoFeB magnetic film for a RF impedance matching was fabricated, and an effect of the loss reduction by introducing a slit-patterned magnetic film was investigated. The fabricated hybrid thin-film coplanar-line device consisted of the top and bottom 5 µm thick copper conductors, an inner (0.5 µm thick polyimide)/(0.15 µm thick CoFeB)/(0.5 µm thick polyimide) trilayer. A signal line width was 6 µm. Total width of the slit-patterned magnetic film was about 200 µm. The devices with some kinds of the width of the magnetic film stripe were fabricated. As a result, insertion loss per unit line length decreased greatly above 1.5 GHz with decreasing width of the magnetic film. The loss suppression was due to an effect of reducing the in-plane eddy current of the magnetic film. On the other hand, the propagation signal-wavelength of the device increased with decreasing width of the magnetic film, which was due to a decrease of distributed inductance. When applying the device to a quarter-wavelength impedance matching device, the slit-patterned magnetic film was effective for decreasing the insertion loss at high frequencies beyond 1.8 GHz.