These are the raw data of Time-domain Thermoreflectance (TDTR) measurements on exfoliated black phosphorus (BP) flakes. The flakes are mechanically exfoliated onto Si substrates and have the thicknesses ranging from 138 to 552 nm. They are encapsulated with ALD-grown ~3 nm alumina layer to prevent possible sample degradation. For TDTR measurements, the samples are further coated with ~70 nm NbV transducer. The through-plane thermal conductivity of the BP flakes along with their two interfactial thermal conductances (at the top and bottom of the flakes) are determined by using conventional TDTR method. We use two different modulation frequencies to adjust the laser thermal penetration depth.