Abstract: A microwave band-pass filter of interdigital type employing microstrip lines and a filter characteristic adjusting method thereof are disclosed. The microwave band-pass filter includes plural stages of resonant lines. Furthermore, the resonant line includes a short-circuit portion, an open portion and a connection portion. The short-circuit portion has its one end grounded and the open portion has its one end open. The connection portion is interposed between the short-circuit portion and the open portion and has its width gradually increased from both sides of the short-circuit portion to both sides of the open portion.