This paper describes a testing method which enables us to determine experimentally the interfacial strength between multi-walled carbon nanotube (MWCNT) and ceramic matrix in MWCNT/ceramic composites. The testing method developed in this research, named "Inclined slit-based pullout method", includes a single nanotube pullout technique and a focused ion beam (FIB) technique, which enables MWCNTs to be pulled out from the ceramic matrix during the pullout tests. Single MWCNTs embedded in a fracture surface of an alumina matrix composite are pulled out using a nanomanipulator system in a scanning electron microscope. Embedded lengths of the MWCNTs are controlled by using the FIB technique, i.e., by making an inclined through-slit near the fracture surface of the composite. The average interfacial strength between the MWCNTs and alumina matrix is evaluated to be 19.2 ± 6.6 MPa for 3 MWCNTs tested in this research. This value is found to be approximately close to that estimated from pullout lengths of the MWCNTs on the fracture surface of the composite, supporting the validity of the testing methods developed in this research.