Background: The Japan Environment and Children’s Study (JECS) is a nationwide birth cohort study of environmental factors affecting children’s health and development. We summarize the complete blood count and chemistry panel statistical data from pregnant women enrolled in JECS. Methods: Statistical data of up to 58,056 mother’s sample in their first (gestational age ≤ 13 weeks) and second trimester (22–27 weeks) were calculated. Results: Mean (SD) values in the first trimester were: white blood cell count, 7866 (1906)/μL; red blood cell count, 417 (33) 104/μL; hemoglobin, 12.4 (1.0) g/dL; hematocrit, 37.1 (2.6)%; mean corpuscular volume, 89.2 (4.7) fL; mean corpuscular hemoglobin, 29.8 (1.9) pg; mean corpuscular hemoglobin concentration, 33.3 (0.9)%; platelet count, 24.8 (5.2) 104/μL; HbA1c, 5.26 (0.26)%; total cholesterol, 181 (28) mg/dL; low density lipoprotein cholesterol, 95 (23) mg/dL; high density lipoprotein cholesterol, 73 (13) mg/dL; free cholesterol, 41 (7) mg/dL; triglycerides, 109 (47) mg/dL; total protein, 6.9 (0.4) g/dL; and albumin, 4.1 (0.2) g/dL. Mean values (SD) in the second trimester were: total cholesterol, 246 (38) mg/dL; free cholesterol, 61 (9) mg/dL; triglycerides, 183 (70) mg/dL; total protein, 6.5 (0.4) g/dL; and albumin, 3.6 (0.2) g/dL. Conclusions: These data will be useful for future JECS studies.