The separation of americium, curium, and the rare earths from high-level wastes by precipitation with oxalic acid was experimentally investigated using synthetic waste solutions and rare earths as chemical stand-ins for americium and curium. Americium, curium, and the rare earths have almost identical chemical properties; hence, practical methods for recovering americium and curium from waste streams are based on two-step procedures in which the first step separates americium, curium, and the rare earth elements from other fission products. In this study, several parameters were investigated over a limited range in continuous-flow experiments (<60 cm3/min) to determine their effect on oxalate precipitation from synthetic waste solutions. Best results were obtained by mixing the waste solution and oxalic acid in one stirred-tank reactor (STR), allowing the oxalate crystals in the resulting slurry to grow in a second identical STR in series with the first reactor, and then separating the solids and liquids by settling or filtration. Yields >90% were regularly obtained. Optimum operating conditions over the range investigated were: liquid residence time per chemical reactor, ≥40 min; final oxalic acid concentration, ≥0.3 M; reactor temperature, ≤25°C; and STR No. 2, stirrer power equal to 0.18 W/ℓ. The stirrer power to the first STR was not found to be an important variable over the range investigated. The experimental results indicate that continuous precipitation of oxalates of trivalent actinides and lanthanides may be feasible. Additional experimental work will be required to determine whether continuous oxalate precipitation is feasible at the high-radiation levels associated with actual high-level wastes.