his study compares the professional liability systems for architects in Taiwan and Japan, examining structural differences in design-supervision obligations, risk allocation, and insurability. Japan's legal framework, through the Architects Act and Building Standards Act, restricts "construction supervision" to technical compliance verification. Regulatory compliance checks are delegated to the review system, clearly defining architects' obligations and maintaining controllable risks. In contrast, Taiwan exhibits an excessive expansion of supervision obligations in public projects while relatively restricting them in private projects. This, coupled with administrative liability spillover and the lack of widespread contractual agreements, leads to escalating uncontrollable risks. This paper constructs a Probability–Impact–Uncontrollability (P–I–U) institutional risk index and conducts a semi-quantitative analysis through a questionnaire survey of Taiwanese architects. Results indicate that the risk index for public project supervision in Taiwan is significantly higher than in Japan, primarily due to the accumulated "uncontrollability" inherent in institutional design. Based on these findings, this paper proposes reforms including limiting supervision obligations, adjusting public project contracts, strengthening administrative reviews, and enhancing insurability.