Palm-based methyl ester sulphonates (MES) is an anionic surfactant derived from palm oil through sulphonation of fatty acid methyl esters. It has good surface-active properties and biodegradability, excellent detergency and is less sensitive to water hardness. It has been used in powder and liquid detergent formulations and other cleaning applications. The evaluation of MES in aquatic ecosystems is vital as they are discharged in large volumes into the environment. An attempt was made to evaluate the acute effect of palm-based MES on Daphnia magna through acute immobilisation studies (48 hr EC₅₀). MES of various chain lengths were selected for the investigation. Based on the results, the EC₅₀ of MES (based on % immobilisation) decreased (became more toxic) with increasing carbon chain length of the surfactant. This trend was also observed in many other anionic surfactants. MES is well suited for environmental-friendly detergent due to its good biodegradability and its toxicity which will not pose any environmental effect on aquatic organisms. The present study provides relevant data concerning the effects of MES surfactant on freshwater invertebrate, which are useful to establish water quality criteria in a regulatory framework.