In this work we present a magnetic study of La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO) nanotubes with nominal external diameters (φ) of 100, 200, 600 and 800 nm. The 800 nm diameter nanotubes have walls of around 50 nm thickness in all the cases. The walls are constituted by an assembly of nanoparticles with a non-Gaussian size distribution presenting a maximum at 24 ± 6 nm (LSMO) and 25 ± 8 nm (LCMO). We carried out isothermal remanent magnetization (IRM) and dc demagnetization (DCD) experiments. We determined that the crystallites are single magnetic domains with a magnetic dead layer on the surface which avoids exchange interactions among grains. We conclude that the dominating interactions are of dipolar type of the same magnitude for all the samples.