In this contribution we report on the influence of Mn doping on various physical properties of Li4Ti5−xMnxO12 (x = 0, 0.005, 0.025, 0.01, 0.05, 0.075, 0.1 and 0.2). Spinel-type (space group Fd3m, a = 0.8358 nm) Li4Ti5−xMnxO12 was produced as highly uniform and polyhedral shaped powder in a size range between 200 and 400 nm. The crystal structure of Li4Ti5−xMnxO12, the morphology and the Mn-ion distribution have been investigated by X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). The oxidation state of Mn and the conductivity behavior of Mn-substituted Li4Ti5−xMnxO12 samples have been studied using multi-frequency electron paramagnetic resonance (EPR). Mn is incorporated as Mn2+, and these ions increase the conductivity of Li4Ti5O12; a conductivity value of 0.48 × 10−8 S cm−1 was measured for Li4Ti5−xMnxO12 with x = 0.075, which is ten-fold larger than that of undoped Li4Ti5O12.