The rate of blood flow in the skin has relevance to several cardiovascular conditions of clinical significance. However, there is no accepted fast, easy way to noninvasively measure the volumetric rate of blood flow per unit tissue volume. Previous work has suggested the potential for using skin heating from radio frequency (RF) energy in the millimeter wave (MMW) band, with simultaneous monitoring of skin surface temperature as a means for noninvasive skin blood flow measurement. This work presents a design and in vitro test results for a simple transducer for MMW blood flow measurement. The transducer consists of a Ka band microstrip antenna and an infrared temperature sensor integrated in a thermoplastic housing. A prototype was tested in a controlled flow chamber, using a commercial tissue phantom material. The device was tested at eight flow rates ranging from 0.25 ml min−1 to 20 ml min−1, equivalent to approximately 10–800 ml min−1·per 100 cm3 of tissue. The differences in temperature increase at exposure time were statistically significant (n = 5) so as to allow resolution of flow rates of 0.25, 0.50, 1.0, 2.0, 10, and 20 ml min−1. The ensemble average of temperature increase versus time over the 60 s exposure window were described by a simple two-parameter lumped model which can be correlated with the flow rate. The flow rate model parameter does not scale directly with the flow in the experimental chamber however. This may suggest limitations either in the model or the experimental procedure.