For companies listed on the Stock Exchange of Thailand (SET), the Securities and Exchange Commission (SEC) is rolling out a plan to bring ISSB standards (IFRS S1 and IFRS S2) into mandatory disclosure requirements, known as the "ISSB Roadmap." Unlike Malaysia (a unified national policy framework) or Singapore (embedded within exchange listing rules), Thailand is taking the approach of gradually upgrading an existing ESG disclosure regime. This article summarizes the latest roadmap, as revised by SEC Thailand in November 2025. 

Existing Foundation: Mandatory ESG Disclosure Since 2022 via Form 56-1 One Report 

Since 2022, all companies listed on the SET have been required to disclose ESG information through Form 56-1 One Report, an annual registration statement that must be filed within three months of fiscal year-end. This is the current baseline, which is more qualitative and flexible than the upcoming ISSB requirements. 

ISSB Roadmap: The November 2025 Revised Timeline 

On 28 November 2025, SEC Thailand published revised principles on the scope and effective timeline, approved by the Capital Market Supervisory Board. Listed companies are classified by SET index grouping: 

• SET50 group (based on the December 2026 index review): begins disclosure in 2027, covering FY2026. 

• SET100 group (based on the December 2027 index review): begins disclosure in 2028, covering FY2027. 

• All remaining SET-listed companies, including new IPOs: phased in gradually, with the goal of having all roughly 800 listed companies disclosing under ISSB standards by 2031 at the latest. 

The specific regulations implementing these principles are still being finalized by SEC Thailand, so the timeline may still be adjusted. 

The "Climate-First" Approach: A Five-Year Transition Period 

Similar to Malaysia, Thailand is taking a "climate-first" approach: for the first five years, companies only need to disclose climate-related information (IFRS S2), before expanding to full sustainability disclosures. Other reliefs during the first five years include: exemption from comparative reporting in the first year, flexibility to report on a different timeline from financial reporting, the ability to use various GHG accounting standards (only GHG Protocol 2004 will be accepted after five years), and disclosing only Scope 1 and 2 emissions before Scope 3 becomes mandatory. 

Assurance Roadmap: Mandatory From Day One 

Thailand requires independent third-party limited assurance for Scope 1 and 2 emissions from the very point a company begins disclosing under ISSB, with no separate deferral period. 

Even though the earliest mandatory milestone is still 2027, there are practical reasons to act now: FTSE Russell already evaluates SET50 companies twice a year, and ISSB readiness directly affects those scores and eligibility for international investment indices; institutional investors are already screening portfolios using ISSB/TCFD-aligned ESG data; and building the necessary data systems and governance processes takes time that cannot be compressed into the final stretch before a deadline. 

What Should Listed Companies in Thailand Do Now? 

• Identify your company's classification group (SET50, SET100, or the remaining group), as each has a different start date. 

• Prioritize building Scope 1-2 emissions data now, as this is the earliest disclosure requirement and requires assurance from the outset. 

• Ensure coordination across departments, including finance, operations, procurement, and legal, rather than leaving this solely to the sustainability team. 

• Plan for climate scenario analysis, a key requirement under IFRS S2. 

• Monitor official regulations closely as SEC Thailand finalizes its revisions. 

The ISSB Roadmap shows Thailand gradually shifting from a qualitative ESG disclosure regime toward international standards with more specific data and assurance requirements. For listed companies, particularly the SET50 and SET100 groups approaching their first mandatory milestones, early preparation matters not just for compliance, but also for access to international capital and ratings from index providers.