Background: Diarrhoea forms major public health problem in children under 5 years of age, especially in developing countries. In Indian slums nearly 100,000 babies die every year before their fifth birthday as a result of dehydration, weakened immunity or malnutrition associated with diarrhea. Aim: To find out the prevalence of Diarrhoea among under five age group in past two weeks and to assess the health seeking behavior of their mothers. Material & Methods: Community based cross-sectional study was carried out from 25th to 31st May,2007 in an urban slum of Delhi. Considering frequency of 3 episodes of diarrhoea/child/year and taking accepted margin of error as 20%, sample size of 695 was calculated. Data was collected in a pre-designed pre-tested Performa by interviewing the mothers of under five children. Data analysis was done by simple statistical tools like percentage. Results: Prevalence of Diarrhoea in last two weeks was about 14.8%. Prevalence of Diarrhoea among under five females 18.4% was highest compared to 12.2% males. 65% mothers knew about use of ORS in Diarrhoea through Private Doctors. (60.2%) cases were given Oral Rehydration Solution (ORS) during diarrhea. 31% mothers knew about ORS but did not know the correct method of preparation and its usage. Breastfeeding was stopped in 43.6% cases. Conclusion: Awareness regarding safe drinking water, excreta disposal and personal hygiene needs to be improved among slum dwellers. Improvement of poor literacy status of mothers is an urgent need to improve their health seeking behaviour and thus the health of their children.