In the past decade, there are Thai population changes initiated by Thai population is clearly a marriage tend to be married shortly. Registration of marriage and divorce registration, less is more. These changes make the Thai people have a smaller family size, because the average age. When the first spouse begins to rise by a survey of the National Statistical Office found that the average age at first marriage of Thai men. In the 24 years old increased from 2513 (1970) is a 27 year 2546 (2003) and girls increased from 22 years in 24 years as 2513 (1970) 2543 (2000) Postponing the age of marriage will affect the reproductive conditions. More Thai people how much slower styling opportunities of children's time, it will be even lower, which will result in a smaller family.