To understand the concepts or principles in mathematics, children who have a concrete operational stage need physical objects that can bridge abstract concepts in mathematics. This research aims to evaluate the influence of coastal contextual learning media on a child's understanding concept in the material of numbers counting operation. This research is a single-case research with the A-B-A withdrawal design. This research used dependent variable in the form of target behavior which consists of the understanding of integer counting operation concept material. Intervention in the form of the use of coastal contextual learning media was independent variable. The media used in this research were seashells that had been colored. The research subjects were 6th graders of one of the primary schools in Tarakan City of North Kalimantan Province, Indonesia. The instrument used to collect the data was a test consisting ten items. The data was analyzed with descriptive statistics in the form of analysis in conditions and among conditions. The research result shows that the coastal contextual learning media in the form of shells was effective to improve the understanding of concept in number counting operation for the research subject. It can be seen from the improvement of the correct answers on the test of understanding concept given.