Abstract: Test results of five concrete beams in fire are presented in this paper, four of which were strengthened with carbon fiber sheet and protected by passive fire insulation, and the other un-strengthened one was tested as a comparison. The primary objectives of these tests are to investigate the influence of flexural cracks at mid span on the temperatures of tensile reinforcements, and to evaluate the failure mode, deformation and fire resistance of the strengthened beams with relatively thin fire insulation. Test results show that: (a) the deflection and crack width and depth of the beam increase very slowly for a long duration of the fire, as a result, the effect of flexural cracks at mid span on the temperatures of tensile rebars is very limited; (b) spalling and debonding of concrete at beam soffit may cause a change of the failure location of the strengthened beam in fire; and (c) in the case that the actual load ratio is not larger than 0.5, the fire endurance of a strengthened beam with relatively thin fire insulation (e.g., 10 mm-20 mm) can meet the requirement of 2h in design code.