Early identification of developmental delays in infants during the first months of life allows for more effective intervention efforts. One way to prevent developmental delays in infants is to provide adequate stimulation through baby massage. This study was conducted to analyze the effectiveness of baby massage on the development of infants 3-12 months in Kamilla Clinic in Gresik Regency. This study is a type of quasi-experiment, by conducting a developmental assessment using the Developmental Scale on 33 infants aged 3-12 months who were selected inclusively. Each infant will be given a massage to determine changes in developmental scores after the intervention. The analysis used to determine the effectiveness of baby massage is the Paired T-Test. The results of the developmental score after the baby massage showed the lowest score of 7 points, there was an increase of 2 points from before the massage. The most improvement occurred in infants aged 6 and 9 months in the category of gross motor, fine motor, and social independence. The results of the analysis of this study indicate that baby massage is effective for improving development in infants aged 3-12 months with a mean of -0.515 with t= -3.55 and p= 0.001. Baby massage is proven to be an effective and fun stimulation method to help the development of infants aged 3-12 months.