Fibers extracted from red algae produced a comparable increase in paper opacity to that produced by experimented inorganic fillers, calcium carbonate. Red algae fibers consist predominantly of cellulose and contain less than 196 inorganic ash. They are comparable to wood fibers in terms of their bonding, combustion, recycling, and biodegradation. While the bonding strength properties of paper decreased with an increase of inorganic fillers in the amount added to the paper, the red algae fibers maintained their bonding properties. These special characteristics seem to stem from the relatively large specific surface areas of the red algae fibers, which are relatively short (0.4-0.8 mm) and narrow (2-4 mu m). Moreover, the addition of red algae fibers to the paper increased the paper stretch and folding endurance in proportion to their added amount. These special properties of red algae fibers may find application in low-basis weight printing paper grades that require high opacity and strength.