Full Text Article (Health Sciences)Background Unacceptably high maternal and perinatal mortality remain a major challenge in many low income countries. Early detection and management of danger signs through improved access to maternal services is highly needed for better maternal and infant outcomes. The aim of this study was to test the effectiveness of an interactive mobile messaging alert system on improving knowledge on danger signs, birth preparedness and complication readiness practices among pregnant women in Dodoma region, Tanzania. Methods A controlled quasi experimental study of 450 randomly selected pregnant women attending antenatal care was carried in Dodoma municipal. Participants were recruited at less than 20 weeks of gestation during the first visit where 150 were assigned to the intervention and 300 to the control group. The intervention groups was enrolled in an interactive mobile messaging system and received health education messages and were also able to send and receive individualized responses on a need basis. The control group continued receiving usual antenatal care services offered at the ANC centers. Pregnant women were followed from their initial visit to the point of delivery. Level of knowledge on danger signs and birth preparedness were assessed at baseline and a post test was again given after delivery for both groups. Analyses of covariance, linear regression were employed to test the effectiveness of the intervention. Results The mean age of participants was 25.6 years ranging from 16 to 48 years. There was significant mean scores differences for both knowleadge and birth preparedness between the intervention and the control group after the intervention (p < .001). The mean knowleadge score was (M = 9.531,SD = 2.666 in the intervention compared to M = 6.518,SD = 4.304 in the control, equivalent to an effect size of 85% of the intervention. Meanwhile, the mean score for IBPACR was M = 4.165,SD = 1.365 for the intervention compared to M = 2.631,SD = 1.775 in the control group with an effect size of 90% A multivariate linear regression showed a positive association between the intervention (p < 0.001) and level of knowledge (B = 2.910,95%CI = 2.199–3.621) and birth preparediness (B = 1.463,95%CI = 1.185–1.740). Conclusion The Interactive mobile messaging alert system demonstrated to be effective in increasing women’s knowledge on danger signs and improving their birth preparedness practices. Keywords: Messaging system, Obstetric and newborn danger signs, Birth preparedness, Antenatal care, Maternal and child health, Health information systems, And mHealth