AbstractWith the recent trends of high‐density packing of electronic circuits and higher‐degree of integration, cross talks between signal lines have become a problem. This paper describes the effect of guard‐shielding on the reduction of crosstalk noises. In relation to the development of our noise evaluation system for printed circuit boards NESSY, the effect of the guard‐shielding was examined by dividing the circuit substrate so that capacitance and inductance of each division is calculated, and by simulating them with a partial element equivalent network. The results were compared with the results of experiments carried out under the same conditions. The experiments and simulations show that: the effect of the guard‐shield depends greatly on the condition of the termination resistances and the termination conditions of the shield; the guard‐shield is effective in reducing the crosstalk noises (e.g., the noise reduces to half even with a thin shield line of the order of 0.1 mm set between the signal lines); it is necessary to ground the shield line at more than two points, since a guard‐line with a single grounding point sometimes even increa