We present a µSR study of oxygen-doped delafossites RCuO 2+δ (δ = 0.5, 0.66; R 3+ = La 3+ , Y 3+ ) which present triangular based lattices of Cu 2+ , S = 1/2 spins. A slowing down of the spin dynamics without onset of a magnetic static freezing down to 1.6 K is found for YCuO 2.5 , which is believed to be an example of a -chain. In contrast, YCuO 2.66 and LaCuO 2.66 clearly order, probably into an antiferromagnetic state, which was rather unexpected.