An anaerobic treatment system that consists of an Anaerobic Filter (AF) and an Upflow Anaerobic Sludge Blanket (UASB) in series was built and operated to investigate its performance in treating strong domestic wastewater with high suspended solids fraction under Jordan's ambient temperatures of 25 degrees C for summer and 18 degrees C for winter. The system was operated from September 2003 until early April 2004. The system was operated at a Hydraulic Retention Time (HRT) of 4 hours for the first stage AF and 8 hours for the second stage UASB. Average COD(t) and COD(ss) removal efficiencies of the AF/UASB were 58% and 81% respectively for the operation period. The results showed that the first stage AF was effective in removing suspended solids. In addition, hydrolysis, acidification and methanogenesis took place in the first stage AF which was advantageous to the second stage UASB. It was concluded that the AF/UASB system is effective in treating strong domestic wastewater with high suspended solids content under Jordan's ambient temperatures.