Background: Life is truly wonderful! In fact, the development of fetus in the womb is just amazing. It is a phenomenon based on strictly regulated alteration of selective and non-selective transcription of DNA and RNA. Selective transcriptions are coupled with proteosynthesis, non-selective with cell division. Fetal growth is the primary method of assessment of fetal well being and is an important determinant of health in later life. Development is related to biological system resulting from a selective, time related switching on and off of genes. Objectives: 1. To assess the knowledge regarding fetal development at various trimesters among antenatal mothers before and after SIM. 2. To associate the level of knowledge regarding fetal development with selected socio demographic variables of antenatal mothers before and after SIM. Materials and Methods: A quantitative research approach was adopted to assess the effectiveness of SIM on knowledge regarding fetal development among antenatal mothers. Quasi experimental non-equivalent control group design was used to assess the effectiveness of structured instructional module on level of knowledge between the variables under each section. The samples were selected by using Non – probability convenience sampling technique. The setting of study in Narayana Medical college hospital and Narayana Superspeciality Hospital, Nellore. Sample size was determined by using single population proportion formula with the assumptions of 95% level of confidence, 10% proportion on knowledge of antenatal mothers on fetal development, 4% of margin of error. Finally considering a non response rate of 8%, the total size was calculated to be 500 antenatal mothers with all trimesters. Among them 250 assigned as experimental group and 250 as control group. Result: The results reveals that effectiveness of SIM considering the overall aspects, antenatal mother’s are gain more knowledge after the administration of the SIM. This 60.82% of knowledge gain is the net benefit of the study which indicates the effectiveness of SIM.