- Electron magnetic resonance (EMR), neutron powder diffraction (NPD) and ac susceptibility techniques were employed for studying the crystallographic structure and magnetic ordering in CaMn1−xRuxO3 (x ≤ 0.40) manganite system. EMR measurements were done on polycrystalline samples at 120 ≤ T ≤ 500 K. High temperature EMR spectra of pristine antiferromagnetic (AFM) CaMnO3 show a singlet Lorentzian-like line, whose intensity diminishes, zeroing at Neel temperature T N=120 K. Strong broadening of paramagnetic (PM) lines with increase of Ru-content (Δ Hpp ∼ 1 T for x=0.10) was found. Upon cooling low-doped (x ≤ 0.06) samples remain AFM, whereas higher doped ones (0.10 ≤ x ≤ 0.40) clearly show progressive appearance of ferromagnetic (FM) phases. Thus, EMR evidences that Ru-doping modifies both PM and AFM states and creates an inhomogeneous phase separated FM and AFM ground states at x0.06. Complementary measurements of NPD and ac susceptibility corroborate the complex character of magnetic ordering, revealed by EMR. The changes of the magnetic ordering in CaMn1−xRuxO3 supposed to be solely determined by doping of Mn-sites with Ru.