The effects of exercise during pregnancy is a major concern for most medical care providers, pregnant women and their families. Numerous studies have recently been conducted on this topic area; however, research findings are inconclusive. Because of this controversy, there is a need to quantitatively and objectively summarize the findings of related studies. The purpose of this study was to analyze existing research studies regarding exercise and birth weight using meta-analysis. The following criteria were used for selecting the published articles: sample size, exercise duration, birth weight, standard deviation, age, experimental group, and control group. Through literature exploration using both computer and hand search strategies, a total of 200 research articles were found to be relevant to the relationship between exercise and birth weight. In-depth screening according to the selection criteria revealed that merely nine of the published studies (a total sample size of 951) had adequate information and were hence included in further analyses. Exercise duration and age were the coding variables. Exercise duration was divided into two levels: those who exercised less than 30 minutes daily for at least three times a week (EX1), and those who exercised 30-60 minutes daily for at least three times a week (EX2). Age was split into two groups: 27-28 years (AGE1) and 29-30 years (AGE2). The weighted effect size (ES) was used in statistical analyses since studies with larger sample size provided superior psychometric properties than those with smaller sample size. The weighted ES for EX1 and EX2 were -.44 and -.04, respectively. EX1 had a larger negative ES value than EX2. This demonstrated that EX1 tended to produce smaller babies than EX2. The weighted ES for AGE1 and AGE2 were -.19 and -.47, respectively. AGE2 had a larger negative ES value than AGE1 indicated AGE2 tended to deliver smaller babies than their counterparts. On the whole, this study supported the notion that pregnant women who exercised 30-60 minutes delivered heavier babies than those who exercised less than 30 minutes. Women in the younger group tended to have larger babies than their older counterparts. Since many researchers have indicated that low birth weight babies are inferior to normal weight babies in many aspects of future growth and development, the findings of this study have emphasized the benefit of exercise during pregnancy. Nevertheless, further investigations on the effects of exercise on birth weight are necessary. Keyword(s): exercise/fitness, health promotion, wellness/disease prevention