One of the central problems of education in Indonesia was the achievement of student learning outcomes that were still needed to be enhanced. It was accordance with the results of preliminary research on the science learning outcome of student in SMPN (State Junior High School) 1 Blega, Indonesia. It was likely due to low process skills. In this study, guided discovery learning model was implemented to investigated the effectiveness of guided discovery learning on students science process skills and students learning outcomes. This study was implemented One Group Pretest-Postest design. The data was analyzed descriptively and the result showed that the persentage of student's mastery learning of science process skill was 100% and student's cognitive learning result was 93%, with increasing in both scores of 71%. The most dominant student activity was science process skill activities (20,07%), supported also by positive student's responses to learning process. This study was proved that guided discovery learning was effective to enhance students science process skills and student learning outcomes.