The new REE-rich, monoclinic, epidote-supergroup minerals ferriakasakaite-(La) and ferriandrosite-(La), found in tephroite ± calcite veinlets cutting the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan, were studied using electron microprobe analysis and single-crystal X-ray diffraction methods. Ferriakasakaite-(La), ideally A1CaA2LaM1Fe3+M2AlM3Mn2+ (SiO4)(Si2O7)O(OH) (Z = 2, space group P21/m), has a new combination of dominant cations at A1(Ca) and M3(Mn2+), which are the key sites to determine a root name for epidote-supergroup minerals. The unit-cell parameters are a = 8.8733(2), b = 5.7415(1), c = 10.0805(3) Å, β = 113.845(2)° and V = 469.73(2) Å3. According to the structural refinement (R1 = 3.13%), the determined structural formula is A1(Ca0.54)A2[(La0.48Ce0.20Pr0.07Nd0.18Gd0.02)Σ0.95Ca0.05]M1(Al0.18)M2(Al0.96)M3(Mg0.07)(SiO4)(Si2O7) O (OH). Ferriandrosite-(La), ideally A1Mn2+A2LaM1Fe3+M2AlM3Mn2+(SiO4)(Si2O7)O(OH) (Z = 2, space group P21/m), is the M1Fe3+ analogue of androsite. The unit-cell parameters are a = 8.8779(1), b = 5.73995(1), c = 10.0875(2) Å, β = 113.899(1)° and V = 469.97(2) Å3, and the structural formula is A1(Ca0.44)A2[(La0.49Ce0.20Pr0.08Nd0.19Gd0.02)Σ0.97Ca0.03]M1(Al0.20)M2(Al0.97)M3(Mg0.10)(SiO4)(Si2O7)O(OH) (R1 = 2.93%). The two new minerals, which are compositionally very similar overall, are distinguished by occupancy of A1, Ca vs. Mn2+. The structural properties of these minerals depend not only on the REE content at A2, but also on the Mn content at A1.