At the second half of twentieth century, regulatory policy of ''Better regulation'' becomes a starting point of developing new regulatory tools in countries being part of an OECD. Considering the benefits and notable results in USA, regulatory impact assessment as an innovative tool of the time, promptly becomes a pedestal of not only regulatory policies in general, but also of an OECD's evidence-based policies in particular. Simplified, in overcoming particular problems and achieving specific public policy targets, RIA can present a whole spectrum of alternatives (based on different data bases), all in favor of harvesting the most suitable solution there is. Ex-ante (preliminary) and ex-post (subsequent) assessment (being part of an regulatory impact tool and regarding their diverse assessing methods) are considered to accomplish different objectives in evaluating outputs of proposed legislation. OECD countries mostly evaluate secondary law initiatives, unlike the Republic of Croatia, which is legally obliged to evaluate primary law initiatives only recommended by the Croatian government. Implementing OECD's principles of good practice, Croatia developed so-called ''two step'' approach throughout which it carries out preliminary assessment (screening RIA) and (depending on the results of direct effect analysis), detailed assessment (full RIA). Subsequent assessment is not a core feature of the mechanism but an exception when it is not possibble to carry out RIA, and consequently, it is prescribed within special laws. Pointed assessments ought to stipulate optimal legal solutions, based on accessible information, which will regulate the subject area, enforce legislative framework, stabilize economy, reduce economy expenses and generate satisfying results towards included shareholders. Hence, regulatory impact assessment becomes internationally recognized as an instrument of empowering legislative frameworks of countries utilizing it, despite exercising different methods of its application. This paper compares key features of the instrument used in OECD countries and the Republic of Croatia, pointing out various application modules and its distinct outcomes.