The present invention provides a hybrid composite sealant, as a sealing material for a planar type solid oxide fuel cell stack, having a matrix of a glass composition, wherein a surface layer reinforced with platelet reinforcement particles is laminated on either one or both surfaces of an inner layer reinforced with fibrous reinforcement particles. Accordingly, by applying the composite sealant of the present invention to the solid oxide fuel cell stack, excellent gas-tightness of the stack can be obtained even under low coupling pressure, thermal cycling durability can be enhanced due to low coupling strength with a contact surface of an object to be sealed, stack disassembly and maintenance can be facilitated when parts within the stack are disabled, and stack stability as well as stack performance can be maintained under a pressurized operation condition where pressure differentials between the inside and outside of the stack reach to 5 atmospheric pressures (0.5 MPa).