Binary melt-blended mixtures of two aryl ether ketone polymers (i.e., a new polyaryl ether ketone) (code name PK99) and poly(ether ether ketone) (PEEK), have been studied. Polymer miscibility in glassy amorphous (or melt) domains has been demonstrated for the binary blend comprising of two aryl-ether-ketone-type semicrystalline polymers. Composition-dependent, single T-g was observed within full composition range in the PK99/PEEK blends, and the narrow T-g breadth also suggests that the scale of mixing was fine and uniform. To better resolve any possible overlapping T-g's, physical aging was imposed on a comparison set of blend samples for the purpose of improving detectability of overlapped multiple transitions if existing. The result still showed one single T-g. The relative sharp T-g and lack of cloud point transition suggest that the scale of molecular intermixing is good. Phase homogeneity was further confirmed using optical and scanning electron microscopy. The X-ray diffractograms suggest that isomorphism does not exist in the PK99/PEEK blends and that the crystal forms of the respective polymers remain distinct and unchanged by the miscibility in the amorphous region.