Research on nature of science (NOS) has confirmed that students' understanding of NOS is best achieved by explicitly considering NOS a cognitive learning expectation and providing opportunities to reflect on it. However, little has been discussed on how to design and use tasks enhancing students' NOS understanding. In an attempt to fill this gap, we analysed the way NOS tasks are used in seven textbooks for a new subject 'scientific inquiry and experimentation' in Korea. The analysis of 84 tasks led to three categories being identified: "guiding to NOS ideas", "expanding NOS understanding" and "thinking critically about NOS". Whereas the majority of the textbook tasks were used as guides to declarative NOS ideas, few tasks invited students to think critically about controversial aspects of NOS. Most tasks were pointed at the epistemic aspects related to scientific methods or knowledge, while the social aspects of science were seldom addressed. Besides, the number and diversity of NOS tasks varied significantly across different publishers. Based on these findings, we call for more strategic and systemic use of NOS tasks in science textbooks, including the use of diverse tasks in proper manners and sequences, as a crucial step to successful NOS instruction in schools.