Few studies have examined reasons why those with low socioeconomic status do not adequately receive cancer screening. We therefore conducted a qualitative study to assess the barriers to cancer screening in people with low socioeconomic status, and to examine the reasons why Medical Aid Program (MAP) recipients do not participate in the National Cancer Screening Program (NCSP). A focus group methodology was used. Participants included MAP recipients (men aged 45-79 years, women aged 35-79 years) who had been invited to cancer screening at least twice based on the NCSP protocol, but had not been screened for any cancer from 2009-2012. We recruited participants living in the cities of Goyang and Paju. A total of 23 MAP recipients participated in four focus group discussions, including 12 men and 11 women. In this qualitative study, we identified six barriers to screening: lack of trust in the NCSP and cancer screening units; fear of being diagnosed with cancer; discomfort or pain from the screening procedure; lack of time, lack of knowledge about cancer screening or lack of awareness of the existence of the NCSP; physical disability or underlying disease; and logistic barriers. Interventions such as individualized counseling, letters and reminders, or other individually-targeted strategies, especially for those with lower socioeconomic status are required to increase participation and reduce disparities in cancer screening.