<p>The Permian and Triassic shallow-water limestones of the Sukhothai Zone, Thailand, are interpreted as remnants of a carbonate platform in the basin of a volcanic arc. This study presents the first report of the limestone units in the eastern Chae Hom area, northern Lampang Province. The Permian limestones are rich in microbial features, oncoids and associated fusulinids and other foraminifers. Lithological descriptions, microfacies analysis and foraminiferal studies allow reconstruction of the palaeoenvironments, depositional setting and age. Three major facies, corresponding to specific depositional environments within the Permian carbonate platform, have been established. These include a well-developed lagoon with small-scale microbial buildups. The fusulinid assemblages are dominated by <i>Pseudofusulina</i> sp. and <i>Misellina</i> sp., with well-preserved late Early Permian smaller foraminifers, indicating a Yakhtashian to Bolorian age. In addition to the Permian limestones, there are Triassic limestones at one new locality in the southern part of the area, consisting of predominantly coated grains, ooids and oncoids. Small foraminifera, including <i>Densophthaimidium</i> cf. <i>americanu</i>m, <i>Endotriada tyrrhenica</i>, <i>Ophthalmidium dannari</i>, <i>Ophthalmidium leischneri</i> and <i>Glomospirella</i>, indicate a Late Triassic (Carnian) age. This evidence of limestone units of different ages in the Chae Hom area resulted from complex tectonic activity during later Triassic times. Consequently, this study is crucial for clarifying the age of the carbonates and for better constraining the palaeoenvironments of the limestones of the Sukhothai Zone, northern Thailand.</p>