Background: Elderly people are vulnerable to malnutrition due to age-related physiological decline, so the knowledge, attitude and practices of them are necessary for the prevention of malnutrition diseases. Aim of the study: To assess knowledge, attitude and practices of elderly people regarding prevention of malnutrition diseases. Research design: A descriptive research design was used. Setting: This study was conducted at Medical Out-patients Clinic in Benha University Hospital. Study subjects: Simple random sample of elderly people including 264 elderly people. Tools of data collection: Two tools were used: Tool (I): A structured interviewing questionnaire sheet which include 3 parts. First part: which included two section; (A): Socio demographic characteristics of elderly people, (B): Current medical health history, Second part: Knowledge of elderly people about healthy nutrition and malnutrition diseases & Third part: Reported practices of elderly people regarding prevention of malnutrition diseases. Tool (II): Likert scale to measure elderly attitude regarding prevention of malnutrition diseases. Results: 38.3% of the elderly people aged from 65 > 70 years old with Mean ±SD (70.51±4.12), 58.7% had poor total knowledge level, 58.3% had satisfactory total practices level and 56.8% had positive total attitude level toward prevention of malnutrition diseases. Conclusion: There was a highly statistically significant correlation between total attitude level of the studied elderly people, their knowledge and their total practices level regarding malnutrition diseases (p<0.001). Recommendations: Conducting health education programs to improve knowledge, attitude and practices about malnutrition diseases and its preventive measures.