This study analyses the effect of sustainability report comprehensiveness level, sustainability report assurance quality, and investor protection level on information asymmetry. We use data from 93 Southeast Asian companies which published sustainability reports during 2015 2017. This study suggests that sustainability report comprehensiveness does not significantly affect information asymmetry. Instead, sustainability report assurance significantly affects information asymmetry. Moreover, higher quality assurance can weaken the negative effect of sustainability report comprehensiveness on analyst forecast accuracy. This study also suggests that a high investor protection level can strengthen the negative effect of sustainability report comprehensiveness on information asymmetry. Sustainability report assurance reduces information asymmetry in countries with strong investor protection levels better. © 2023 Inderscience Enterprises Ltd.. All rights reserved.