Reproduction and especially lactation are nutritionally costly for mammals. Maternal access to adequate and optimal nutrients is essential for fecundity, survival of offspring, and offspring growth rates. In eutherian species energy requirements during lactation can be heavily dependent on litter size and the body mass of the female. In marsupials litter size does not appear to affect nutritional requirements during lactation; however, studies ofmarsupial nutritional requirements during lactation are rare. Marsupials are distinct from eutherians as they give birth to young at a much more underdeveloped state and the majority of their investment into the growth of their offspring occurs postnatally. Nutritional requirements of adult female red-tailed phascogales (Phascogalecalura) were measured to determine the differences between those lactating and not lactating. On average females that were lactating had maintenance energy requirements of 1728 ± 195 kJ kg−0.75 d−1, double that of non-lactating animals. There was no significant correlation between energy requirements and litter size among lactating female phascogales. Apparent absorption of macronutrients did not differ between lactating and non-lactating individuals. The study has shown that food needs to be increased by at least double during late lactation. Litter size appears to have no influence on maternal nutrient requirements when food is available ad libitum and offspring in smaller litters grow faster than those in larger litters.