Objectives: This study aimed to throw some light on knowledge, attitude and the histological changes in human placenta exposed to passive smoking. Methods: Hospital-based studies were conducted to assess the knowledge and attitude of passive smoking in pregnant women and non-smoker controls (n=50) were selected. A structured questionnaire was used for data collection. Differences between the 2 groups were determined by the Chi-square test and the significance level was set at p<0.05. Total 50 placentas were collected immediately from interviewed pregnant women after delivery (38-40 weeks of gestation) from the Department of Obstetrics and Gynecology. According to the result yielded from the questionnaire 20 out of 50 placentas, showed no history of exposure to tobacco smoke, or consumption of tobacco in any form, and were labeled as controls. About 30 placentas were collected from passive smokers mostly exposed to smoke. The pregnant mother exposed to tobacco used by a chain-smoking husband or very close relative in a nuclear family was designated as a passive smoker. Results: The study indicated that there are significant statistical differences found among the pregnant women’s on their knowledge, attitude in term of pregnancy outcome and adverse effect on labor. The placenta exposed to passive smoking showed an increase in the connective tissue stroma in chorionic villi (intravillous fibroid) and some of them lost their trophoblastic covering. Also, the lumen of blood capillaries appeared obliterated and irregular. Conclusion: Our findings suggested that quantitative parameters of the placenta significantly showed changes in placenta from the passive smoker group compared to the controls. These changes can probably be associated with pregnancy complications in smoking mothers and may affect the development and survival of the fetus and even it’s future.