The insurance industry plays a crucial role in the development of the country's economy. Hence, it is imperative to ensure the financial well-being and effective administration of insurance businesses in Indonesia. Underwriting Result is a crucial factor in determining the economic performance of insurance businesses. This study investigates the impact of Claim Reserving in CoB for Marine Hull, Fire, and Engineering on Underwriting Results. Multiple Linear Regression analysis examines the effects of claim reserving in class of business (COB) for Marine Hull, Fire, and Engineering on Underwriting Results. Furthermore, if the values of Claim Reserving in CoB for Marine Hull, Claim Reserving in CoB for Fire, and Claim Reserving in CoB for Engineering are all 0, then the Underwriting Result value is 750,646,258,2008. Because this model can only explain around 35% of the variance, more studies should be conducted by including additional variables such as operational expenses, claims incurred, and other variables that influence underwriting results. © 2026 Author(s).