The purposes of this research was to study the effect of Deductive and Inductive teaching with Creating and Solving problem practice formats in Web-Based Instruction on Mechanical Equilibrium content of Physics upon Critical Thinking mathayom suksa IV students. The subjects were 160 mathayom suksa IV students of Khon Kaen University Demonstration School, during the second semester of 2007 academic year. They were randomly grouped by Basic Physics examination results into 4 treatment groups, 40 students in each group. These 4 treatment groups were randomly according to 4 difference types of Web-Based Instruction as: (A1) Deductive teaching with Creating problem practice format, (A2) Deductive teaching with Solving problem practice format, (B1) Inductive teaching with Creating problem practice format, and (B2) Inductive teaching with Solving problem practice format. The research instruments were the 40 multiple choice Items of Mechanical Equilibrium, which were adapted from Cornell Critical Thinking Test Level z, and the 4 difference types of Web-Based Instruction with two units of Mechanical Equilibrium content. The Data were analyzed by mean of 2-way Analysis of Variance at the 0.05 level of significance.

The research results were as follows:

1. There was no statistical significant difference effect between Deductive teaching and Inductive Teaching in Web-Based Instruction upon Critical Thinking of mathayom suksa IV students at the .05 level of significance.
2. There was statistical significant difference effect between Creating problem and Solving problem in Practice format in Web-Based Instruction upon Critical Thinking of mathayom suksa IV students at the .05 level of significance.
3. There was statistical significant interaction effect between the Teaching method and Practice formats in Web-Based Instruction upon Critical Thinking of mathayom suksa IV students at the .05 level of significance.