Low levels of physical activity (PA) are of a health concern among high body mass index (BMI) women living a sedentary lifestyle and being overweight or obese during pregnancy is associated with increased risks of maternal and fetal health complications. Obstetricians often provide advice regarding recommended PA levels, yet this has not been easily achieved in this group to prevent adverse birth-related outcomes. The purpose of this study is to explore motivators/enablers and perceived barriers through in-depth qualitative inquiry, guided by a behavioral change model, for understanding of pregnant women’s decisions to engage, or refrain from PA practice. Thirteen overweight and obese pregnant women aged 28 to 45 years with an inactive, sedentary lifestyle in urban areas of northern Taiwan were recruited to participate in six focus group sessions for their intent and readiness for PA engagement in pregnancy. A thematic content analysis was performed with a constant comparison method to categorize interview data and generate themes. The findings illustrate the extent to which obese and overweight pregnant women’s readiness for PA is affected by multiple factors, including personal beliefs, perceived societal norms, peer support, and the competing priorities in the environment. PA interventions are to be effective by focusing on overcoming barriers, increasing motivations, and enhancing self-management. Strategies shared by participants shed lights for program developers to design preferable behavioral interventions for this group of women who are low self-esteem with low self-efficacy to increase PA and meet recommended levels. There is considerable potential for health care providers to provide accessible information, facilitate PA, and promote an active lifestyle during and after pregnancy.