21Linear alkylbenzenes (LABs) as sewerage indicators were investigated in the sediments of the 22 West and South Peninsular Malaysia. Surface sediment samples were analyzed using gas 23 chromatography-mass spectrometry. Results showed that LAB concentration in the samples 24 of Port Dickson and the Kim Kim River varied from 111.6 to 255.8 and from 88.2 to 119.0 25 ng•g −1 dry weight, respectively. The ratios of internal isomer, in which the benzene ring was 26 close to the center of the linear alkyl chain, to external isomer, in which the benzene ring was 27 near the end of the linear alkyl chain (I/E ratios), of LABs in Port Dickson coast sediments 28 ranged from 2.6 to 4.1. By contrast, the ratios for sediment from the Kim Kim River varied 29 from 1.7 to 1.9. I/E, long-chained LABs over short-chained LABs (L/S), and C 13 /C 12 ratios 30 indicated that the aquatic environment received primary and secondary sewage effluents. These 31 findings emphasized the necessity of continued water treatment system development in 32 Malaysia.33