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 and an inner (0.5 μm thick polyimide)/(0.15 μm thick CoFeB)/(0.5 μm thick polyimide) trilayer. A signal linewidth was 6 μm. The 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.