BACKGROUND: Newborns having birth weight less than 2500 gms (2.5 kg) is defined as low birth weight (LBW) newborns, measurement being taken preferably within the first hour of life (WHO-1994). Out of 23 million LBW infants, 7-10 million LBW babies are in India, which constitutes about 30% of live births per year. OBJECTIVE: This study was conducted to identify and quantify the effects of weight, height and body-mass index (BMI) of mothers, responsible for LBW of babies. MATERIALS AND METHODS: The study was a case-control study, performed in a RTHC of kishanganj district, Bihar, from November-2013 to December-2013. A total of 360 newborns (120 cases and 240 controls) were selected for study during the study period. Every singleton newborn baby having birth weight <2.5 kg was included as a case and those having birth weight >2.5 kg were included as control in this study. The relation of birth weight of newborns to few maternal factors, such as weight, height and BMI, were studied. STATISTICAL ANALYSIS: This was done in SPSS 17. Odd's ratio with 95% confidence interval was calculated. RESULTS: In this study, we observed that mothers having weight less than 45 kg were having 5.45 times (OR= 5.45) more chances of getting LBW babies. Similarly, mothers having height less than 145 cm and BMI <18.5 were having 2.46 times (OR=2.46) and 3 times (OR=2.91) more chances of having LBW babies, respectively. CONCLUSION: This study concluded with the findings that weight, height and BMI of mothers was strongly related with LBW of newborns. Hence, it is necessary to strengthen the existing maternal services at the basic level of the community.