This study examines the influences of three inquiry-based instructions (structured inquiry, guided inquiry and open inquiry) on tenth graders' scientific inquiry abilities, including posing questions and hypothesis, planning, experimenting, collecting and analyzing data, and interpreting and concluding. The three inquiry-based instructions used in this study are based on the different amount of teacher guidance in a topic related to weather observation. The participants in this quasi-experimental research were three classes of tenth graders (43 students in structured inquiry, 43 students in guided inquiry, and 41 students in open inquiry) in Taipei County. Here are the results. (1) Students' overall scientific inquiry abilities had no significant difference before and after the inquiry-based lesson, but their performances were improved obviously in posing questions and hypothesis (t = 3.56, p ＜0.0001, E.S.= 0.81). (2) The low-inquiry-ability students made more significant improvement than the medium-inquiry-ability and high-inquiry-ability students in the overall inquiry ability after the inquiry-based lesson. (3) The structured-inquiry instruction was the most helpful to improve the ability in posing questions and hypothesis; especially, it helped the low-inquiry-ability students improve their abilities in experimenting, collecting and analyzing data. (4) The guided-inquiry instruction helped the low-inquiry-ability and medium-inquiry-ability students improve their ability in posing questions and hypothesis. Also, the guided-inquiry instruction improved the medium-inquiry-ability students' ability in planning, and the low-inquiry-ability students' ability in interpreting and concluding. (5) The open-inquiry instruction improved the high-inquiry-ability students' ability in planning. (6) More than half of the students perceived the classroom learning environment closer to their expectation after the inquiry-based instructions. In present science classroom, most students have few chances to undertake student-centered inquiry. It is suggested that teachers adopt suitable methods of inquiry-based instruction in order to promote students' inquiry abilities.