A matrix modification was studied for the determination of trace manganese in several seaweeds by electrothermal atomic absorption spectrophotometry(ETAAS). The type and quantity of modifiers were investigated to realize the efficient modification. Palladium was chosen as a single modifier. By the addition of palladium(5$mu extrm{g}$/$mell$) to 2ng/$mell$ manganese solution, the temperatures were raised from 1,00$0^{circ}C$ to 1,20$0^{circ}C$ for the charring and from 2,10$0^{circ}C$ to 2,20$0^{circ}C$ for the atomization as well as the sensitivity and reproducibility were improved. With such optimum conditions, the trace amount of manganese in several seaweeds(laver, tangle and brown seaweed) could be determined by a calibration curve method, and good recoveries of more than 965 were also obtained in the samples in which a given amount of manganese was spiked. The detection limit of this method was about 0.048ng/$mell$.