The purposes of this study were 1) to examine the level of the students' awareness of environmental conservation and critical thinking, and 2) to compare the awareness of environmental conservation and critical thinking of the students of different genders and GPA. The samples were 70 first-year students from Faculty of Environment and Resource Studies, Mahasarakham University, enrolled in the course "Foundations of Environmental Education", in the first semester of academic year 2010. The research instruments consisted of a measurement of the students' environmental awareness questionnaire and a critical thinking test. The results revealed that in overall the students' awareness of environmental conservation was at the moderate level (x = 3.9096). The average score (x = 8.7360) of critical thinking was less than 50 % of the total test scores. By considering genders and GPA levels, there was no difference in the students' awareness of environmental conservation. When considering each individual domain of critical thinking, the students of different genders showed difference in the average score of 'recognition of assumptions' domain (p<.05). It was also found to be significant (p<.05) in the "inference" domain in the students with different GPA.