The study of formal logic helps to improve the process of thinking and tries to refine and improve the thinking ability. The objectives of this study are to know the effectiveness of formal logic course and to determine the critical thinking variables that are effective and that are ineffective. A sample of 214 students is selected from all the three departments Engineering, Information Technology and Business department from Nizwa College of Technology, Sultanate of Oman. The analysis revealed that there is no significant relationship between critical thinking variables and formal logic course. It is found that deductive and interpretation skills of the students have increased after the posttest. At the same time, inference skills, assumptions and arguments decreased after the posttest. Assumption skill is found to be the most favourable critical thinking variable.