In the present study, biosorption of stable cobalt was studied in an up-flow fixed-bed column using the brown alga Sargassum glaucescens treated with fon-naidehyde (FA) or MgCl2. Notable increase in cobalt removal was observed for FA-treated biosorbent with 2.7 and 1.4 times higher dynamic capacity (DC) and uptake capacity (UC) than native alga, respectively. Consequently, FA-treated S glaucescens was selected for further investigations. In particle size experiments, the DCs of 0.5-1 and 1-2 mm particles were both equal to 27.6 mg/g, and corresponding UCs were 34 and 38 mg/g, respectively. The maximum DC was obtained at residence time of 2.5 min. Studying the effect of additional ions indicated partial effect of Na+ and K+ ions on DC and UC, Mg2+ reduced highly the DC and slightly the UC while heavy metal ions (Ni2+, Cd2+, Cu2+, Zn2+, Pb2+ and Cr3+) caused decrease in both DC and UC about 1.5-4.7 and 1.8-3.2 times, respectively. Moreover, the column regeneration studies were carried out for four sorption-desorption cycles. The DC and the UC highly decreased in the second cycle, partially decreased or remained constant in the third and in the fourth one.