This study is focused on the microfacies and facies associations in the 540 meter-thick interval of the Late Permian Upper Dalan reservoirs in the South Pars Gas Field using the petrographic studies, image analysis techniques and quantitative analysis of the constituting components. The petrographic studies led to the recognition of 15 microfacies that formed in four facies associations: peritidal, lagoon, shoal and off shoal. Due to the high frequency of the shoal facies in the Upper Dalan, those have been investigated in details. The relative sea-level changes during deposition of the Upper Dalan member were examined using the vertical microfacies and facies association’s variations. The main focus of this study is to investigate the microfacies variations and depositional environment evolutions in the Upper Dalan member in response to the relative sea-level changes. The frequency analysis of the facies revealed that during the Late Permian, a major fall has been occurred in relative sea-level recorded in the lower (K4 unit) and upper (K3 unit) parts of the Upper Dalan member. In these intervals, the facies change from ooid-bioclastic shoals to the alternative layers of shoal-lagoon-peritidal facies. As well, anhydrite precipitation and dolomitization are prominent diagenetic features, which are indications of climate change. The facies variations were used to reconstruct the relative sea-level changes during deposition of the Upper Dalan member in the South Pars Gas Field. As a result, two and a half third-order and 12 fourth-order cycles have been distinguished.