Objective:To investigate the correlation between growth and development situation of mandibular second molar and individual biological age among male and female teenagers in Chongqing. Methods:The study subjects are consisted of 357 teenagers in the Department of Orthodontics in Stomatological Hospital of Chongqing Medical University. The root length（RL）

crown width（CW）and length（CL） of mandibular second molars（Msm） were measured by cone beam computed tomography（CBCT）

and the specific values related to above parameters were calculated. The Pearson correlation was applied to analyze the above values of the third molar and age

and the paremeters with high relevance were selected to establish equations for the use of age assessment with accuracy verification test. Results:The Pearson correlation coefficient revealed significant relationships between RL

RL/CW and CL/RL of Msm and chronological age of the three groups(For RL

r

male

=0.659

P=0.000;r

female

=0.572

P=0.000;r

all

=0.608

P=0.000. For RL/CW

r

male

=0.580

P=0.000;r

female

=551

P=0.000;r

all

=0.543

P=0.000. For CL/RL

r

male

=-0.497

P=0.000;r

female

=-0.448

P=0.000;r

all

=-0.470

P=0.000)

Furthermore

the linear regression equations between age（Y）and RL（X

1

）

RL/CW（X

2

）and CL/RL（X

3

）were established as follows:Y

MALE

=4.165+0.341X

1

+2.151X

2

+0.882X

3

（P=0.000

R

2

=0.547）;Y

FEMALE

=5.057+0.255X

1

+2.938X

2

-0.160X

3

（P=0.000

R

2

=0.466）;Y

ALL

=4.918+0.285X

1

+2.521X

2

+0.240X

3

（P=0.000

R

2

=0.499）. The relative errors of age assessment using those regression equations in male

female and both groups were 5.00%

5.90% and 5.46% respectively. Conclusion:There is significant relevance between growth and development situation of mandibular second molar and individual biological age among male and female teenagers in Chongqing. Taking those parameters as indicators to establish equations provide a novel idead for the research of age assessment.