We propose a new electromagnetic shielding (EMS) sheet that uses carbon nanotube (CNT)-composite paper. The electromagnetic environment in which electronic devices such as mobile phones and personal computers operate has become increasingly complex due to increased electromagnetic noise. This noise can cause unexpected behavior in electronic devices. Therefore, EMS sheets are required to shield devices from this noise. Carbon-nanotube composite paper has high electrical conductivity despite being a paper and does not deteriorate like metallic materials which are commonly used for EMS sheets. In this study, we aim to use CNT-composite paper to develop new EMS sheets that have a high shielding effectiveness (SE) (over 30 dB) at frequencies in the 0.1 MHz to 1 GHz range. To achieve this, we made test samples and measured their SE with the Kansai Electronic Industry Development Center (KEC) method. The first CNT-composite paper we developed achieved an SE of 20-50 dB from 0.1 MHz to 100 MHz. However, the SE was 16 dB in the GHz band. To increase the SE in this band, we designed and simulated many different shapes of shielding sheet which we then fabricated to measure their SE. We obtained positive results, indicating that a new shielding paper shape has a higher SE in the GHz band.