The low-temperature (60 K) beta-gamma phase transition in deuterated malonic acid single crystals is studied by electron-nuclear double resonance (ENDOR) and ENDOR-detected nuclear magnetic resonance (EDNMR) methods. The results are compared with new neutron diffraction data. Crossing the transition temperature from the high-temperature beta phase to the gamma phase results in a broadening of the Lines and an eventual doubling of their number in the EDNMR and ENDOR spectra. From the analysis of EDNMR angular dependencies, it follows that during the transition every second molecule rotates about the c axis by approximately 2 degrees. The characteristics of the phase transition are discussed.