<p>Fiscal rules are designed to enhance fiscal discipline and macroeconomic stability, but their influence on investments remains inconclusive in the literature. This study investigates the existence of nonlinear effects of the number of fiscal rules adopted on aggregate, public and private investment. This nonlinearity is expressed through an inverted U-shaped relationship between the number of fiscal rules adopted and investment, suggesting that the adoption of fiscal rules may be beneficial to investment, while their excessive proliferation may reduce investment. Special attention is given to developing countries, which often exhibit lower levels of fiscal responsibility and are more sensitive to the constraints and incentives created by fiscal rules. The study explores whether excessive adoption of such rules may hinder investment. The study also analyzes public investment as a mechanism for transmitting the impact of fiscal rules on private investment. The study uses a database composed of 105 countries (70 developing countries and 35 developed countries) from 1990 to 2021. Estimates for the full sample and the sample of developing countries, as well as for aggregate, private and public investment reveal the existence of an inverted U-shaped relationship between the number of fiscal rules and investment. By identifying a structural nonlinear relationship, the study contributes to a deeper understanding of how fiscal rules affect investment. The findings offer insights for designing balanced and effective fiscal frameworks.</p>