The purpose of this research is to produce guided discovery-based mathematics learning material that valid, practice and effective.This research uses Plomp model which is proposed three stages of developmentc: preliminary research, development or prototyping phase and assessment phase.Data validity analysis showed that guided discovery-based mathematics learning material resulting in extremely valid category because the learning material had a good validity both the content and construction side. In data practicability analysis showed that discovery-based mathematics learning material is practical because it can be applied well in math learning process. The use of discovery-based mathematics learning material could make the students more active in the learning process which can be seen from their classroom activity. Moreover, the level of final result completeness increased up to 78.13%. It means that this device is effective in improving students’ final result. In conclusion, this research, guided discovery-based mathematics learning material, is valid, practical and effective.