This study examined relations between multiple measures of maternal iron status assessed 3 months post-partum, and infant processing speed (longest look during visual habituation), memory (novelty preference), attention (heart rate changes), and neural response variability (in auditory event-related potentials) at 3 and 9 months. Plasma iron was associated with 9-month novelty preference and longest look, and developmental changes in longest look. Hemoglobin predicted sustained attention, and both plasma iron and soluble transferrin receptors predicted neural response variability at 9 months. Improved maternal iron appears to have a positive impact on infant cognitive development even in a well-nourished, low-risk sample.