The purpose of this research was to study the ability of scientific reasoning of 10^th grade students in Suphan Buri Province. The sample were 194 10^th grade students in Suphan Buri Province. The research instrument was scientific reasoning ability test that improved from Lawson's classroom test of scientific reasoning: multiple choice version (Lawson, 2000). The collected data were analyzed by mean, percentage and standard deviation. The data revealed that 10^th grade students in Suphan Buri province had low average scores of scientific reasoning abilities (mean equals to 3.41).