Assessing a child's growth through the observation of his/her developmental milestone requires a team effort, in which family plays an important role. To assess the knowledge of the Iraqi mothers regarding their children's developmental milestones of their children and to find out if there was any association between this knowledge and certain demographic variables. A cross sectional study, that extended for one year period with sample size of 400 mothers attending six primary health care centers in Baghadad for maternal and child health care. Data were obtained by using a questionnaire derived from the (developmental checklists birth to five 2012), it was composed of four domains of knowledge (motor, cognitive, language and social) in addition to the demographic information of the participated mothers. The data were then analyzed by SPSS version 22; Pearson`s chi square test was used to used to detect the significance of association between categorical data accordingly and the mother's knowledge in each domain and every socio-demographic variable (p value ≤0.05 was regarded significant). Regarding the age of the mothers, the majority were between 20-29 years old (40.5%), 70% of them were employed and the illiterate mothers constituted (30.25%) of the study sample. Most of the mothers (71.5%) stated that their experience was their main source of information. There was a significant association was observed between the mothers age and all four domains of knowledge, other variables (education level, source of information, employment, Number of children, Residence of family) showed different levels of association and most of the mothers had a limited knowledge regarding the cognitive domain.