Phenolphthalein poly(ether ether ketone) (PEK-C) was found to be miscible with uncured tetraglycidyl 4,4'-diaminodiphenylmethane (TGDDM), which is a type of tetrafunctional epoxy resin (ER), as shown by the existence of a single glass transition temperature (T-g) within the whole composition range. The miscibility between PEK-C and TGDDM is considered to be due mainly to entropy contribution. Furthermore, blends of PEK-C and TGDDM cured with 4,4'-diaminodiphenylmethane IDDM) were studied using dynamic mechanical analysis (DMA), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). DMA studies show that the DDM-cured TGDDM/PEK-C blends have only one T-g. SEM observation also confirmed that the blends were homogeneous. FTIR studies showed that the curing reaction is incomplete due to the high viscosity of PEK-C. As the PEK-C content increased. the tensile properties of the blends decreased slightly and the fracture toughness factor also showed a slight decreasing tendency, presumably due to the reduced crosslink density of the epoxy network. SEM observation of the fracture surfaces of fracture toughness test specimens showed the brittle nature of the fracture for the pure ER and its blends with PEK-C.