The  purpose of  this research was 1) to construct the Module instruction for  Mathayomsuksa  three students to meet the  probability  effectiveness criterion at 80/80. 2) to compare students achievement before and after studying by using the module instruction and 3) to compare students achievements between studying by using the module instruction group and expository teaching group.
The samples were 80 students of  Mathayomsuksa  three in the second semester of the academic year 2009 at  Prajuntrarajbumrung  school in Prajantakam District, Prachinburi Province. The research instruments were the module instruction, an achievement test and mathematics learning plans on  module instruction  and  expository teaching method. The statistical analysis employed was percentage, arithmetic mean, standard deviation and t-test.
The results of the research were as follows 1) the effectiveness of module instruction was 83.22/82.50. 2) The students achievement on studying  by using the module instruction was higher than before with a statistical significant level .05 and 3) The students achievement on studying  by using the module instruction was higher than using the expository teaching method at .05 as well.
