Students bring with them their own misconceptions to the science classes and it becomes a barrier in developing new concepts. Therefore, identifying misconceptions is an essential component in teaching science. The objective of this study was to identify 10th grade students' misconceptions on plant transport with the use of two-tier diagnostic test. The development procedure of the two-tier diagnostic test had three steps; (i) defining the content boundaries of the test (ii) collecting information on student misconceptions and (iii) instrument development. Student alternative conceptions were collected after interviewing 25 students and multiple choice questions with free responses being administered to the students. With the use of the date obtained, sixteen (08) two-tier multiple test items were constructed. The first tier examined the content knowledge and the second tier the reasons for the content. The conceptual knowledge examined in the test items were water absorption, mineral salt absorption, transportation of water, transpiration, organic food transportation. The diagnostic test was administered to 180, 10th grade students. It was revealed that students possessed 18 misconceptions. The highest number of misconceptions was recorded in the areas of organic food transportation and the transpiration. The most common misconception was found in the area of organic food transportation.