High-yield pulps (HYPs) can be used in the production of high-quality fine paper grades. In such applications, optical brightening agents (OBA) and inorganic fillers, such as precipitated calcium carbonate (PCC) may be used to improve the paper properties, including optical properties, such as brightness, whiteness, opacity. In this study, some fundamental parameters regarding OBA and PCC adsorption onto pulp fibers were investigated. Results showed that OBA was preferably adsorbed onto bleached kraft pulp (BKP) fibers than onto HYP fibers when present in a mixed furnish. The OBA adsorption at a low adsorbed amount followed the Langmuir adsorption isotherm for both BKP and HYP; the adsorbed OBA in a monolayer was more for the BKP than for the HYP. The PCC adsorption behaviors on the same two pulp systems, however, are different from those of OBA: the HYP had more PCC adsorption than the BKP. The results on the adsorption of PCC onto the HYP and kraft pulp fibers showed that they also followed the Langmuir kinetics very well.