Single crystals of Ln2Ru3Al15+x (Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6K followed by a likely incommensurate-to-commensurate transition at 14.9K for crystals oriented with H//ab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H, indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects. Single crystal, structure, and highly anisotropic magnetoresistance due to strong crystalline electric field effects of Tb2Ru3Al15.05. Display omitted •Single crystals of Ln2Ru3Al15+x were grown for the first time via flux growth.•The structure of Gd2Ru3Al15.09 differs from that of arc melted Gd2Ru3.08Al15.•Tb2Ru3Al15.05 exhibits highly anisotropic magnetic and transport properties.•The properties of Tb2Ru3Al15.05 arise due to crystalline electric field effects.