Abstract: The studies are based upon the samples of five-toet jerboa (Allactaga sibirica) collected from Huhohoat district from March to October 1980 and 1987.A total number of 556 specimes were collected,among which 324 were males and 232 females.With the lens weight of five-toet jerboa as the age criteria,7 age groups were recognized.The standerds of these age groups were listed below:Group 1 juvenile:The lens weight was less than 55.00 mg.Group 2 Subadult:The lens weight was 55.01-77.50 mg.Group 3 Adult (Ⅰ):The lens weight was 55.01-87.50 mg.Group 4 Adult (Ⅱ):The lens weight was 87.51-102.50 mg.Group 5 Adult (Ⅲ):The lens weight was 102.51-117.50 mg.Group 6 Adult (Ⅳ):The lens weight was 117.51-130.00 mg.Group 7 Senil:The lens weight was more than 130.00 mg.The subadults were born from June to October this year.The adults (Ⅰ) were collected before June or the breeding was collected after June.This paper shows that body weight,body length and tail length are not suitable for the age indicators of five-toet jerboa.Five-toet jerboa is an animal in hibernal sleep,that is from October to March of next year.Before June the collected specimens all were born in the last year and two years ago.The greater part of five-toet jerboa breed one time in the year.In this year the born juveniles and subadults appeared in July,August and September.The specimens of the adult (Ⅰ-Ⅳ) and the older were collected in June,that were born in last year,the year before last year,two,three and four years ago respectivelly,so to the five-toet jerboa can live five years old,but the most of them only live two to four years.