ABSTRACT The objective of research is to find out: (1) the implementation of International-Level School Pioneering (RSBI) program in mathematics learning in SMA Negeri 1 Cilacap, (2) the obstacles encountered in the implementation of International-Level School Pioneering (RSBI) program in mathematics learning in SMA Negeri 1 Cilacap, and (3) the measures taken to cope with the obstacles encountered in the implementation of International-Level School Pioneering (RSBI) program in mathematics learning in SMA Negeri 1 Cilacap. This research employed a descriptive qualitative method. The research was taken place in SMA Negeri 1 Cilacap in the School Year of 2008/2009. The data source in this research was obtained from the results of interview, observation activity and documentation. The sample of research was taken using the purposive sampling technique of 5 math teachers and 11 students of grade X. The data validation was done using method triangulation to examine the validity of the implementation of International-Level School Pioneering (RSBI) program in mathematics learning and data or source triangulation to examine the validity of the obstacles in the implementation of International-Level School Pioneering (RSBI) program in mathematics learning as well as the attempts of coping with them. Technique of analyzing data employed was qualitative data analysis encompassing data reduction, display, and verification as well as conclusion drawing. Based on the result of research, it is obtained that the implementation of International-Level School Pioneering (RSBI) program in mathematics learning in SMA Negeri 1 Cilacap is as follows (1) teacher undertakes the math learning activity using lecture method accompanied by the question-answer and assignment with bilingual learning as well as using Information and Communication Technology (ICT)-based learning media with power point program, (2) the students’ activity tends to follow the teacher activity learning by preparing the material or dictionary/ alfalink so that the learning process is still teacher-centered, (3) the assessment is measured from the cognitive and affective aspects based on the values of assignment, daily examination, mid-semester examination and end-semester examination, the questions of which are written in English. The obstacles encountered in the implementation of RSBI program in mathematics learning include (1) the teachers have limited English and ICT capability so that they are difficult to deliver the lesson material and the students are difficult to comprehend the material in English, (2) the obstacles the school encounters concerns the infrastructure availability and the perception on RSBI shared between the school members and society. The measures taken to cope with the obstacles encountered in the implementation of RSBI program include (1) the teachers attend English and ICT training, comparative study program, workshop or RSBI seminar and conduct real teaching along with the facilitator and make an discussion in MGMP forum, (2) the students attend Student English Club and prepare the dictionary or alfalink to master the math terms in English, and (3) the school makes a socialization to the school members and society about RSBI as well as improves the facility.