Maternal nutrition is impacted by personal and environmental factors including dietary intake, knowledge, food availability, and affordability. This cross-sectional analysis aimed to evaluate nutrition-related knowledge, attitudes, practices, and associations with hemoglobin concentration among lactating mothers in the Bukavu region, Democratic Republic of the Congo. In 444 lactating mothers, nutrition-related knowledge and practice were assessed by questionnaires and translated into knowledge and practice scores ranging from 0 to 1, attitudes and drivers of food choice were assessed, the Dietary Diversity Score (DDS) was assessed with 24 h dietary recalls in a potential range from 0 to 10, and hemoglobin (Hb) was measured in mothers and their infants. Anemia prevalence was 28.2% among mothers and 74.3% among infants aged 3–8 months. Nutritional knowledge and practice were limited (the median total knowledge score was 0.39, median DDS was 3.0). While there were slight positive correlations between knowledge and maternal Hb, DDS did not significantly correlate with either knowledge or Hb. Although half of the mothers stated a perception about their own susceptibility to anemia or vitamin A deficiency (56.4%, 47.4%), less than half of those could justify their estimation (40.9%, 44.2%). Taste (68.1%), appearance (42.5%), availability (29.0%), and health effects (25.6%) were important drivers of food choice. In conclusion, interventions on the different influencing factors including nutrition education strategies are needed.