The purpose of this research was to know effect of Problem Based Learning to Improving Oral Cummunication skill and Student’s Cognitive Result in Grade X SMA Negeri 1 Purbolinggo in Plantae topic. The method for this research was a pretest-posttest design, using a purposive sampling technique, with a total sample of 72 students and analyzed by t-test. The research results showed that oral communication skill for experiment group is 82,05 (very good) and for control group is 69,72 (good). Student’s cognitive result for N-Gain experiment group is 0,50 (moderate) and for control group is 0,30 (low) with Sig. (2-tailed) t-count < 0,05. Therefore, Improving Oral Cummunication skill and Student’s Cognitive Result in Grade X SMA Negeri 1 Purbolinggo with Problem Based Learning in Plantae topic is significantly.