Introduction: Happiness is accounted for one of the psychological health criteria, and it is person's judgment from satisfaction of quality of life. Pregnancy is an experience that changes physical, social and mental of women. But the attitude of women towards their pregnancy are important and for a woman who has healthy pregnancy according to psychological, it is a Manifestation of a sense of self-actualization and feminine identity. This study aimed to determine the related factors with happiness in pregnancy. Aim: To determine factors associated with happiness in Pregnancy Methods: In this study, 300 low risk pregnant women who have referred to health centers for prenatal care, were selected by multistage sampling and demographic questionnaire, history of midwifery, lifestyle, Oxford happiness questionnaire and the personality traits of NEO- FFI complete. Content validity of the questionnaire was performed and the reliability was measured with Cronbach's alpha. Data were analyzed with spss software and Spearman and Pearson correlation coefficients, Kruskal-Wallis, Mann- Whitney tests and One- way ANOVA were used. Results: The mean age of subjects 25.1 years, with a standard deviation of 4.9 at the age of 18 to 35 years. The frequency of low, medium and high level of happiness was 11.3%, 72.5%, and 16.2% respectively. Happiness are related to employment status (p0.002, chi-square= 12.9, df= 2), exercise (p=0.000 and Z=3.36), entertainment (p= 0.043, f= 3.3, df= 78), duration of Religious activity (p=0.001, F=1.8, df=2), Neuroticism (p=0.000 and r=0.294), Extroversion (p=0.000 and r=0.289) Conclusions: Regarding to importance positive emotions such as happiness in mental health, programs is recommended for promotion of related factors in pregnancy .