In situ catalytic upgrading is a promising technique to improve the properties of bio-oil because the bio-oil produced from the conventional method has several negative attributes, such as low heating value and highly acidic nature, and is also unstable during storage. In this study, the catalytic effect of CaO, MgO, and ZSM-5 as in situ upgrading catalysts during biomass pyrolysis was studied in a fluidized-bed reactor. Southern pine sawdust was subjected to pyrolysis with inert bed material (quartz sand) and subsequently with the catalysts. The quality of bio-oil obtained was compared to the baseline values (i.e., with the use of sand as bed material without any catalyst) in terms of its chemical composition, heating value, viscosity, pH, total acid number (TAN), and oxygen and water contents. The use of CaO resulted in an improvement in pH (2.393.98) and TAN (88.946.6) of the bio-oil when compared to the results when using only sand. In comparison, MgO was a mild catalyst because it altered the bio-oil quality slightly, while ZSM-5 had no effect on the acid content in bio-oil, although it produced bio-oil with the least oxygen content at a significantly lower yield and higher water content (38.5%). In terms of chemical composition, the catalysts exhibited different behaviors to various groups of compounds. Anhydrosugars were reduced by all of the catalysts tested to different extents, but CaO significantly altered the quality of bio-oil by reducing organic acids, while CaO and ZSM-5 reduced the abundance of phenolic compounds with a higher oxygen content. An accelerated aging test was performed to compare the efficacy of these in situ catalysts on improving the stability of bio-oil, and it was observed that the bio-oil produced using CaO was the most stable when compared to the baseline and other catalytic bio-oils tested in this study.