We investigated the composition of the milk of the quokka between 70 and 300 days post partum. From 70 to 180 days, the mean concentration of protein in the milk was 63.5 ± 6.50 g L-1. The protein levels then began to increase, peaking at 120 g L-1 towards the end of lactation. The mean lipid and total solids content were 45.0 ± 6.50 and 175.0 ± 11.77 g L-1 from 70–180 days, increasing to 150 and 250 g L-1 after permanent pouch exit. In contrast, the total carbohydrate concentration of the milk decreased from 80 to 20 g L-1 at 150 days. The concentration of lactose started to decrease at 180 days from 30 to 10 g L-1, and galactose and glucose began to rise from 1 to 9 g L-1 and 0.5 to 4.0 g L-1, respectively. The milk lipid consisted mainly of long- and medium-chain fatty acids, with no short-chain fatty acids detected. The major fatty acids present were palmitic and oleic acids, followed by linoleic, trans-vaccenic and stearic acids. The percentage composition of oleic and stearic acids varied significantly during lactation. The composition of the milk of the quokka changed during lactation, coincident with the young reaching critical milestones in its development. This finding supports the hypothesis that the composition of the milk changes to meet the nutritional needs of the developing young.