Hydrogenolysis of consumer-grade high-density polyethylene (HDPE) is a pivotal strategy for upcycling plastic waste into value-added fuels. Though Ru catalysts demonstrated activity in the hydrogenolysis of inert C–C bonds of HDPE, the precise design of Ru nanoparticles still represents a critical challenge to boost the performance. Here, ultrafine Ru nanoparticles (∼1 nm) supported on MgAl-layered double oxides (MgAl-LDO) exhibited a selectivity over 90% for liquid fuels, lubricants, and waxes in the hydrogenolysis of HDPE. By tuning the thermal treatments and Mg/Al ratios, the Ruδ+/Ru0 ratio and acidity/basicity of MgAl-LDO were determined as critical performance descriptors. Notably, the confining effects of the layered structure of MgAl-LDO can be optimized to facilitate the effective dispersion of Ru nanoparticles, even at elevated loadings of up to 9%. Moreover, the Ru/Mg1Al-LDO catalyst exhibited good applicability in the hydrogenolysis of various HDPE substrates and excellent stability, maintaining the structure and activity in five recycling runs.Ru/Mg1Al-LDO catalysts with stabilized ultrafine dispersed Ru nanoparticles are highly efficient in the conversion of consumer-grade high-density polyethylene wastes into valuable alkanes for sustainable fuel production.