This study aims to determine the ability of critical thinking and biology learning outcomes through the application of guided inquiry learning This research is a classroom action research (PTK), with descriptive analysis. Subjects in this study were students of class X ATP 4 SMK Negeri Pertanian Pekanbaru which amounted to 28 students consisting of 23 male students and 5 female students. The result of data analysis of critical thinking ability of students obtained in the first cycle is 78% with category critical enough increase of 1% in cycle II to 80% with critical category. Results of data analysis and cognitive learning outcomes for the absorption of students before the PTK is 71.7%, after PTK 72.2%, then an increase of 0.5% before the PTK. Absorption of students in the second cycle of 73% occurred in increase of 0.8% of the cycle I. Student classical completeness before the PTK is 39%, after the PTK in the first cycle of 61%, then an increase of 22% from before the PTK, and Classical mastery in cycle II is 64%, then there is an increase of 3%. Based on the results of the study showed that the application of guided inquiry learning can improve the ability of critical thinking and cognitive learning outcomes of biology of class X students ATP 4 SMK Negeri Pertanian Pekanbaru