The implementation of standard Integrated Management of Childhood Illness (IMCI) is still experiencing problems in the field. One of the contributing factors is the lack of knowledge, skills, and experience of health workers in optimally handling illness infants or toddlers. The purpose of this study was to identify the effect of training in the management of illness toddlers with the IMCI approach on the behavior of health workers in the management of illness toddlers. This study used a Quasi-experimental research design using a pre-post-test design with one group. Thirty health workers were a participant on duty at the Medan Sunggal Public Health Center using purposive sampling. Data were collected by a demographic data questionnaire, and questionnaire on knowledge, attitudes, and observation sheets to measure actions about IMCI. The univariate analysis was descriptive statistical analysis to present the characteristics of the respondents and the behavior of health workers in handling illness childhood under the IMCI approach. The bivariate analysis was inferential statistical analysis, namely, the Wilcoxon test was used to compare the behavior of health workers in handling illness childhood with the IMCI approach before and after being given IMCI training. The results showed that the management training for illness toddlers with the IMCI approach was effective for the knowledge of health workers in the management of illness toddlers (p-value 0.0001), the training for the management of illness toddler with the IMCI approach was effective for the attitudes of health workers in the management of illness toddlers (p-value 0.0001). Training on the management of illness toddlers with the IMCI approach was effective for the actions of health workers in the management of illness toddlers (p-value 0.0001).