Science Process Skill (SPS) on the biology learning can facilitate student to reach the science learning and push student to find their own concept of knowledge, facts along with develop attitude and values. The purpose of this research is to improve student's at class XI IPA 2 of SMA in skin excretory system using guided inquiry. Participants in this reasearc is 36 student of class XI SMA in Karanganyar who choose science program. The target of this research is to increase percentage of each skill indicator on SPS about ≥10%. The result of this research shows an the average percentage on student's SPS increasing from 29,78% to 65,34%. But, in the classification skill need to be trained more intensively, because it has not reached the target. Based on the result above the conclusion that guided inquiry can improvement student's SPS participant.