Low　birthweight　(LBW)　is　closely　associated　with　fetal　and　perinatal　mortality　and　morbidity.　We　identified　the　risk　factors　of　LBW　and　geographical　differences　in　LBW　incidence　in　30　Chinese　provinces　in　the　present　study.　This　study　was　a　population-based,　retrospective　cohort　study　performed　in　30　Chinese　provinces.　We　used　data　from　the　free　National　Pre-pregnancy　Checkups　Project,　which　is　a　countrywide　population-based　retrospective　cohort　study.　To　identify　regional　differences　in　LBW　incidence,　we　used　the　Qinling-Huaihe　climate　line　to　divide　China　into　northern　and　southern　sections　and　the　Heihe-Tengchong　economic　line　to　divide　it　into　eastern　and　western　sections.　Multivariate　unconditional　logistic　regression　analysis　with　SAS　9.4　was　used　for　data　analysis.　P＜.05　was　considered　statistically　significant.　LBW　incidence　was　4.54%　in　rural　China.　Southern　China　had　a　significantly　higher　incidence　(4.65%)　than　northern　China　(4.28%).　Our　main　risk　factor　for　LBW　is　paternal　exposure　to　radiation　(odds　ratio=1.537),　which　has　never　been　studied　before.　This　study　identifies　multiple　risk　factors　of　couples　giving　birth　to　LBW　babies　including　paternal　risk　factors.