Mn-based Heusler alloys of NiMnSb and PtMnSb have been predicted to be half-metallic ferromagnetic metals, with 100% spin-polarized conduction electrons at the Fermi level. In this study, the valence-band and Sb 4dcore levels of the XMnSb-type Heusler alloys (X = Mi, Pd, Pt) have been investigated using synchrotron-radiation photoemission spectroscopy. Samples were made by melting the appropriate amount of constituent elements in vacuum-sealed quartz tubes at 1100 °C, and subsequent annealing at 600 °C for one week. Photoemission measurements were performed on the Mark V beamline at the Synchrotron Radiation Center at the University of Wisconsin-Madison. Polycrystalline samples were fracturedin situand measured at about 60 K in a vaccum better than 4 × 10−11Torr. The instrumental resolution of the system is about 0.2 eV athν=40 eV and about 0.4 eV athν= 150 eV, respectively. The incident photon flux was monitored by the yield from a gold mesh and all the spectra were normalized to the incident photon flux. Due to the photon energy dependence of the photoionization cross sections, the valence-band spectra around 120 and 150 eV in PdMnSb and PtMnSb, respectively, can be considered to represent the Mn 3dpartial spectral weight (PSW) distribution. The extracted Mn 3dPSWs of PdMnSb and PtMnSb are found to be very similar to each other. The measured Sb 4dcore level spectra are very similar for NiMnSb and PtMnSb. In contrast, the Sb 4dspectrum for PdMnSb is less structured, as compared to NiMnSb and PtMnSb, indicating a larger lifetime broadening and a smaller surface core level shift in PdMnSb.