Malnutrition remains a critical public health issue, particularly in low- and middle-income countries (LMICs), contributing to over 50% of under-five mortality. Severe acute malnutrition (SAM) affects millions of children, leading to life-threatening complications and long-term developmental impairments. Maternal knowledge plays a pivotal role in preventing and managing SAM, yet gaps persist in awareness and healthcare access. This study assessed mothers' knowledge of SAM at Sher-e-Bangla Medical College Hospital (SBMCH), Barishal, Bangladesh. A descriptive cross-sectional study was conducted among 60 mothers of SAM-affected under-five children admitted to SBMCH’s Nutrition Corner. Data were collected via semi-structured questionnaires and analyzed using SPSS version 16.0. Descriptive statistics and chi-square tests were employed to examine associations between socio-demographic factors and maternal knowledge. Ethical clearance and informed consent were obtained. The majority of mothers (57%) had primary education, while 31.7% of fathers were illiterate. Only 61.7% recognized a balanced diet combined with breastfeeding as optimal supplementary food, and 28.3% consistently practiced handwashing before food preparation. Despite 93.3% living near health centers, only 5% attended medical checkups. Television was the primary information source (56.7%), yet 38.3% had never heard about malnutrition. Significant associations were found between maternal knowledge and age (*p* = .002), education (*p* = .010), paternal education (*p* = .004), and income (*p* = .041). Maternal knowledge on SAM prevention is inadequate, influenced by education, income, and healthcare access. Targeted interventions, including community-based education and media campaigns, are urgently needed to improve nutritional practices and reduce SAM prevalence in rural Bangladesh