The dynamic range, sensitivity and dark decay of holographic recording in LiNbO3 crystals doped with 0.2 atomic% Mn with different oxidation states have been measured. The sensitivity is 0.5 cm/J and found to be independent of the oxidation states, while the largest M/# obtained is 12/mm (extraordinary light polarization, light wavelength 458 nm). The dark. decay time constants of non-fixed holograms stored in these LiNbO3:Mn crystals obey an Arrhenius-type dependence on the absolute temperature with an activation energy of about 1.0 eV, and the dark decay is several orders of magnitude slower than that of LiNbO3:Fe with comparable doping levels. In contrast to LiNbO3:Fe, the dominant dark decay mechanism in highly-doped LiNbO3:Mn crystals is due to proton compensation rather than electron tunneling.