Background: Behavioural habits develops from adult through imitation where as other as purposeful movements. Where children cannot adjust to complex environment around them, they are unable to grow in the socially acceptable way resulting in the exhibition of particular behaviour and this is known as behavioural problems. Objective: (1) To assess knowledge regarding behavioural problems among mother of preschool children in selected rural areas. (2) To associate the knowledge score with their selected demographic variable. Methodology: Quantitative Descriptive research design was selected to conduct study. 60 mothers of preschool children were selected as samples based on exclusion and inclusion criteria through non-probability purposive sampling technique. Result: The 91.7% of mothers of preschool children had poor level of knowledge score, 8.3% of mothers of preschool children had average level of knowledge score. No mother of preschool children had a good or very good level of knowledge score. The result also reveals that the mean is 3.61 and standard deviation 1.29. Analysis also reveals that there is no association of knowledge score with age, education, occupation, religion, monthly family income, number of children, type of family and source of information. Conclusion: Thus, it was concluded that, majority of mothers of preschool children have a poor knowledge score regarding behavioural problems of children, hence it is suggested that the interventional studies can be conducted in future to raise the knowledge of mothers regarding behavioural problems of preschool children.