Problem statement: To identify demography factor relation that is study, education storey; level, mother age and also social economics status to occurrence of LBW in RSCM Jakarta. Approach: Type this studied is analytic survey with cross sectional design. Population in this studied is all noted mothers bear during year 2006 counted 2.755 with sample equal to 125 mothers. This studied is started in January with intake of sample by random sampling. The data were collected in this studied are secondary data, that is seen data and noted from medical record of RSCM Jakarta Year 2006. Appliance used at this studied is sheet of check list. Data analysis conducted by univariat and bivariate. Results: Statistical test from variable studied that is, study, education, mother age and social economics status, known by that there is relation having a meaning among study of mother, mother age and social economics status with occurrence of heavy baby born to lower in RSCM Jakarta. Conclusion: LBW in RSCM Year equal to 4.54% from 125 mother sample bear.