The electrical conductivity of monocrystalline triphylite, Li(Fe²⁺,Mn²⁺)PO₄, with the orthorhombic olivine-type structure was measured parallel (∥) to the [010] direction and ∥ [001] (space group Pnma), between ∼400 and ∼700 K. Electrical measurements on triphylite are of technological interest because LiFePO₄ is a promising electrode material for rechargeable Li batteries. Triphylite was examined by electron microprobe, ICP atomic emission spectroscopy, X-ray diffraction, Mössbauer spectroscopy and microscopic analysis. The DC conductivity σ_DC was determined from AC impedance data (20 Hz–1 MHz) extrapolating to zero frequency. Triphylite shows σ_DC with activated behavior measured ∥ [010] between ∼500 and ∼700 K during the first heating up, with activation energy of E _A = 1.52 eV; on cooling E _A = 0.61 eV was found down to ∼400 K and extrapolated σ_DC (295 K) ∼10⁻⁹ Ω⁻¹cm⁻¹; ∥ [001] E _A = 0.65 eV and extrapolated σ_DC(295 K) ∼10⁻⁹ to 10⁻¹⁰ Ω⁻¹cm⁻¹, measured during the second heating cycle. The enhanced AC conductivity relative to σ_DC at lower temperatures indicates a hopping-type charge transport between localized levels. Conduction during the first heating up is ascribed to ionic Li⁺ hopping. DC polarization experiments showed conduction after the first heating up to be electronic related to lowered activation energy. Electronic conduction appears to be coupled with the presence of Li⁺ vacancies and Fe³⁺, formed by triphylite alteration. For comparison, σ_DC was measured on the synthetic compound LiMgPO₄ with olivine-type structure, where also an activated behavior of σ_DC with E _A ∼1.45 eV was observed during heating and cooling due to ionic Li⁺ conduction; here no oxidation can occur associated with formation of trivalent cations.