The Carbon Intensity Indicator (CII) regulation is a short-term measure of IMO for reducing GHG emissions from ships. In addition, the 2023 IMO GHG Strategy describes that the CII regulation is anticipated to create a potential synergy effect with other measures. Accordingly, the CII regulation, which took effect in 2023, is forecast to increasingly impact international shipping and the commercial vessel market. However, efforts to improve energy efficiency and implement slow steaming for ships are insufficient to meet the CII regulation that is increasingly stringent over time. Therefore, there is a growing need for fundamental improvements in future response strategies. In this study, major causes of low CII ratings for ships were investigated from a recent consulting project that was conducted to support shipping companies in satisfying the regulation from operational and technical perspectives. Lastly, proposals to implement the CII regulation effectively and to reduce GHG emissions from ships fundamentally were made, taking into account the major causes derived from the consulting.