Sphingosine-1 phosphate (S1P) receptor–modulating therapies from the new generation of oral small molecules represents a milestone in the evolution of the therapeutic armamentarium followed by two decades of monoclonal antibodies. S1P receptors have been proposed as a therapeutic target for IBD due to their involvement in the regulation of lymphocyte trafficking out of lymph nodes and into sites of inflammation in gastrointestinal tract. In 2021. ozanimod was the first S1P receptor modulator approved by the FDA and EC for the treatment of moderate-to-severe UC. With the introduction of S1P receptor modulators in the therapeutic landscape of IBD, more options are offered to patients and clinicians. Still, we are witnessing continuous progress in this field with the development of promising second-generation drug classes that are in the final stages of clinical study. The results of the phase 2 clinical trial of patients with UC published in 2019 indicated the efficiency of the new S1P receptor modulator etrasimod and were the basis for several ongoing phase 3 studies (ClinicalTrials.gov Id: NCT03996369, NCT04176588, NCT03945188, NCT04173273). The aim of this research is a development and validation of a green analytical method for quality control of etrasimod as an integral part of the preformulation stage crucial for the consistent efficacy of a drug product. The analysis was performed at Agilent 1260 UHPLC system using Phoroshell C18 (3.0×100 mm, 2.7 µm) column at 25°C. The mobile phase consisted of water and acetonitrile acidified with formic acid (0.1%) and delivered with a gradient system (flow: 1 mL/min). The quantitation was performed at 227 nm. Analytical GREEnness metric approach software was used for greenness score evaluation. The system suitability parameters were measured by injecting a standard solution (6 µg/mL) in six replicates (retention time: 3.66 min, peak area: 131.8 mAU, plate count: 31550, and symmetry: 1.0). The RSD values were less than 1%, thus leading to a high degree of accuracy of the system. The validation was performed according to ICH Q2(R1) guidelines. The peak purity was higher than 999. The high linearity (range: 2-10 µg/mL ; r=0.999) was observed. Precision was studied as repeatability with six analyses within the first day (RSD≤0.73%) and as intra-day precision with three analyses for three days (RSD≤0.82%). Accuracy was tested on three concentration levels to confirm the applicability of the method in the whole range (99.0-100.4%). The method showed an acceptable green score (0.8). The validated green method represents useful support for preformulation studies essential for the development of robust and effective dosage forms. The work was funded by the Croatian Science Foundation (HRZZ-UIP-2017-05-3949).