The old theories cannot explain the decreasing of the mortality, from 123/100o in the mid of 1960 to 48 in the mid of 1980. The Hmong population in northern Thailand still has high fertility and rarely uses the modern health care service. Most of the Hmong lives in the remote villages and live with the cultivation with their own labour. The Hmong women have education in low level. The structure of family is the patrichal extended family. The women are in low status. These are opposite to Thais which the rate of mortality is decreased because the family planning is popular. The fertility is rapidly decreased. The modern health care is popular. The educational level is rapidly increased in both sex. The economy is highly developed and most of them is single families. The Hmong data shows the model of the mortality following the old theories which are the high rate of mortality and the elderly gravida. However, the infants who early get born and a group of teenage mother are not found this relation whereas the recent cohorts are found the mortality and the death of fetus decreased in every birth order and very age group of the mothers. There are a few of the Hmong women who labour with the modern medical care service. In addition, there is no any difference between the death rate of male and female infants. The ethnicity evidences suggest that there are Hmong traditions for well protecting and taking care of the mothers and their infants in every age group when labour and every birth order without exception. Furthermore, the Hmong are pleased to accept the new innovation which is good for the health of th mothers and the infants. These factors increase the higher chance for the infants survival.