© 1965-2012 IEEE. This paper discusses the distribution of magnetic flux density inside a magnetic film covered on a microstrip line for developing a design rule of the magnetic-film-type noise suppressor. The measured and simulation results of the magnetic field distribution and conduction loss agree with each other. The distribution of magnetic flux density B inside the magnetic film can be confirmed numerically through the theoretical calculation of the characteristic length including the complex permeability of the magnetic film. These results demonstrate that the complex permeability of the magnetic film leads to a complex characteristic length and distributed magnetic poles and results in the alternated distribution of B vectors along the distance. These results also suggest that these distributed magnetic poles are required when the inductive crosstalk and conduction loss are considered in the design of patterned magnetic-film-type noise suppressor. Based on these results, this paper could be of great use for the quantitative evaluation of crosstalk between the aggressor and victim lines.