We have measured the diameters of the Cepheid variablesCephei (18 nights) and � Aquilae (11 nights) with the Navy Prototype Optical Interferometer. The primary results of these observations are the mean angular diameters hLDi of these Cepheids: 1.520 ± 0.014 milliseconds of arc (mas) forCep and 1.69 ± 0.04 mas forAql. We also report limb-darkened diameters for the check stars in this program: forLac, �LD = 1.909 ± 0.011 mas, and for 12 Aql, �LD = 2.418 ± 0.010 mas. When combined with radius estimates from period-radius relations in the literature, the Cepheid angular diameters suggest distances slightly smaller than, but still consistent with, the Hipparcos distances. Pulsations are weakly detected at a level of ∼ 1.5� to 2� for both Cepheids.