Fast pyrolysis technology is currently moving forward to commercialization, and demonstration plants are at the commissioning stage. The quality of bio-oil differs significantly from fossil fuels, and therefore, upgrading technologies are needed to improve the fuel properties of bio-oil. Co-processing of bio-oil in refinery fluid catalytic cracking (FCC) would have many economic advantages compared to other upgrading technologies because no essential modifications to the refinery are needed. However, because of its different chemical composition, the introduction of bio-oil into the FCC unit will introduce uncertainty to the refinery operation. In this paper, co-processing of dry thermal bio-oil, catalytic pyrolysis oil, and hydrotreated bio-oil was compared using a micro activity test (MAT) setup. The experiments show that the bio-oil concentration during co-processing should remain low to avoid high coke formation. Co-processing of dry bio-oil also resulted in a much lower liquid yield compared to catalytic pyrolysis oil and hydrotreated bio-oil. This was probably caused by the higher amount of sugar-like material in the dry bio-oil. The differences between catalytic pyrolysis oil and hydrotreated bio-oil were relatively small, except for the coke formation tendency, which was higher for the more aromatic catalytic pyrolysis oil.