The undoped ScAlMgO4 crystal was synthesized by the Floating Zone (FZ) method, and we evaluated the optical and scintillation properties. The transmittance spectrum showed the absorption edge around 200 nm. VUV-excited emission/excitation spectrum was characterized at a synchrotron facility (UVSOR). Our experiment revealed that the emission was around 400 rim by 200 nm excitation, and the excitation band was 170-210 nm for the latter emission peak. The decay time characterized by 280 nm excitation was 8.3 and 43 ns. Under X-ray irradiation, an emission was observed around 400 nm as for VUV excitation, and the latter decay time constants were 0.23 and 2.2 mu s. In addition, the afterglow level at 20 ms after X-ray irradiation was around 0.1% of the intensity during irradiation.