Nanotechnology is an emerging science that involved in different fields. This research inquired elementary school students' learning effect by using quasi-experiment, expositive-teaching and experiential-teaching methods for nanotechnology in the microcosmic world. By utilized the pretest "Nanotechnology Situational Questionnaire (NSQ)", we have selected 110 fifth grade students with similar academic performance in nanotechnology knowledge from Northern Taiwan. This research designed 2 teaching steps. The first step had 4 class sessions, and then implemented the expositive-teaching to all the students. The main learning context was related to understand nanometer definitions, characters and fundamental concepts. The second step divided 110 students into treatment and comparison groups, each group had 3 class sessions. The treatment group implemented experiential-teaching, on the other hand, the comparison group implemented expositive-teaching by PowerPoints, animations and movies. After the experiment, the 2 groups completed posttest NSQ. The results showed: 1. Two groups were no difference in posttest NSQ score after the first step teaching, but after the second step teaching, the treatment group had significant higher scores than comparison group. It meant that experiential-teaching method was more effective than the expositive-teaching. 2. In expositive-teaching: (a) Used actual objects, students held more complete concepts and had significant learning effect. (b) The simulated model teaching facilitates learning, but students somewhat still had vague concepts. (c) Applied a simulated model to explain another simulated model, students can hardly understood difficult concept, so they still had misconceptions. Therefore, before teaching, teacher must considering cognitive development and selecting teaching methods carefully. For extensive nanotechnology education and foster talents, educators must adopting nanotechnology into formal elementary curriculum and designing a series of complete teaching plan. (Contains 6 tables and 1 figure.)