Purpose: The purpose of this study was to evaluate the cognitive effects of chemotherapy in patients with breast cancer. Methods: Using several databases, prospective studies were collected up to August 2011. Of 2,106 publications identified, 12 met the inclusion criteria, and 8 studies were used to estimate the effect size of chemotherapy on cognitive impairment. Results: Twelve studies were done since 2005 and most of the research was performed in Europe or North America. Eight studies were used to generate effect size across the cognitive domains of attention/concentration, verbal and visual memory, executive function, visuospatial skill, language, and subjective cognitive function. Each of the cognitive domains showed small effect sizes (-0.02 ~ -0.26), indicating diminished cognitive function for the chemotherapy group compared with non-chemotherapy groups. Conclusion: Finding suggests that breast cancer patients who undergo chemotherapy may experience mild cognitive decline. Further study is needed to generate knowledge and guideline for interventions to address chemotherapy related cognitive impairment in these patients.