Preweaning mortality risks, recorded death reasons and related factors for preweaning mortality were studied in 105 breeding herds. Preweaning mortality risk at the herd level was calculated as the difference between the number of pigs born alive in farrowed litters and the number of weaned pigs divided by the number of pigs born alive in litters that farrowed and weaned. The mean of annual preweaning mortality risk was 10.7%. In regression analysis, higher mortality risks were associated with higher parity at farrowing, greater numbers of pigs born alive, and longer lactation length. The period from July to September had a higher mortality risk than that from April to June. The means of cause-specific proportional mortality ratios (PMR) in trauma with low viability and scours were 80.4 and 6.2%, respectively. Sows with pig age 0-1 day during lactation had the highest daily PMR. Sows with pig age 0 to 7 days had higher PMR due to trauma and low variability than those with pig age 8 days older. Sows with pig age over 7 days had higher PMR due to scours than those with pig age 0-7 days. Careful management at farrowing and in early lactation on high parity sows with large litters should be considered to prevent piglets from death due to trauma and low viability, and appropriate herd health programs should be implemented for reducing preweaning mortality due to scours during late lactation.