Background and Aim: Pregnancy in low age ranges could be risky and planning supportive programs is critical for pregnant youths. Therefore, this study aimed to explore the effectiveness of Teasdale cognitive therapy (based on mindfulness) on the reduction of anxiety, stress and depression among pregnant woman younger than 20 years of age. Methods: This study employed pre-post-test method with the control group. The study population included all pregnant women of Ardebil who was below 20 years of age and who reported higher than normal level scores in anxiety, stress or depression during 2013. The selected sample comprised 30 youth pregnant females below 20 years age. They were selected by convenience method from health care centers of Ardebil, and assigned randomly in control and experimental group. The data collected by standard anxiety, stress and depression questionnaire and trait anxiety. The collected data were analyzed by multiple analysis of variance (MANOVA). Results: The result of MANOVA revealed that mindfulness based cognitive therapy (MBCT) significantly is effective on stress (F [1,29] = 57.58 P < 0.0005), anxiety (F [1,29] = 57.58 P < 0.0005) and depression (F [1,29] = 79.52 P < 0.0005) of pregnant women who aged below 20 years. Conclusion: According to the findings of this study and other relevant studies as pregnancy is a very sensitive stage of every woman's life and they need proper care. The authors suggest to future researchers to design and explore MBCT based on pregnancy condition associated problems.