The aim of the present study is to investigate the causes of single-childhood in mothers with a child. The research method was qualitative and phenomenological. The number of research samples was determined by data saturation, which was finally achieved by interviewing the twelfth person. Purposive sampling was used to select participants. The data collection tool in this study was a semi-structured interview, designed by the researcher, which was conducted after confirming the face validity of the main interview. Thematic analysis was used to analyze qualitative data. In this study, 58 subcategories with themes and 10 main categories were obtained. The categories obtained from the interviews were categorized into two parts: mothers' perceptions of single-childhood (pleasantness and unpleasantness) and causes of single-childhood (individual, interpersonal, sociocultural, and economic). This category showed that some mothers were satisfied with their situation of having one child, and the rest were worried about their future and their child who had no companion. Also, their concern about being alone indicated dissatisfaction with the current situation.