In spite of extensive experimental studies of the angular-dependent magnetoresistance (ADMR) of the low-temperature phase (LTP) of α-(BEDT-TTF)₂ KHg(SCN)₄ about a decade ago, the nature of LTP remains elusive. Here we present a new study of ADMR of LTP in α-(ET)₂ salts assuming that LTP is unconventional charge density wave (UCDW). In the presence of magnetic field the quasi-particle spectrum in UCDW is quantized, which gives rise to striking ADMR in UCDW. The present model appears to account for many existing ADMR data of α-(BEDT-TTF)₂ KHg(SCN)₄ remarkably well.