In this review paper, the use of inorganic fillers in cellulosic paper with some unique functions, such as magnetic, photocatalytic, flame retardant, antibacterial, deodorizing, electrically conductive, and thermal buffering properties, is highlighted. Notably, fillers and cellulosic pulp fibers can sometimes exhibit synergic effects on special applications, such as photocatalysis. The methods associated with the use of fillers can include direct wet end addition, lumen loading, in situ synthesis of filler particles in the presence of cellulosic pulp fibers, formation of fiber/filler composites, and surface filling. Also, regardless of the end uses of the paper products, the general methods for modifying fillers or the papers with fillers can reasonably include nanoengineering, chemical modification, surface encapsulation, mechanical modification, and formation of filler-based composites, etc. The use of cellulosic fibers as carriers of these inorganic fillers for specific functions can create more opportunities for using abundant cellulosic fiber material.