This study investigated the effects of test-wiseness training in Mathematics on adolescent secondary school students' test anxiety. The research study adopted for the study was an experimental research that involved pretest, posttest and control groups design. One hundred and twenty (120) adolescent senior secondary school class three students of Ondo State public secondary schools selected through stratified random sampling technique formed the sample. These participants were randomly assigned to experimental and control groups. Experimental group was made to undergo the test-wise training package in Mathematics (TTPM), which lasted for six weeks, while 'placebo' was used on the control group. Two instruments were used to collect data. They are Adolescent Students' Test Anxiety Scale (ASTAS) and Adolescent Students' Test-wiseness Scale in Mathematics (ASTSM). Three research questions were raised translated into two hypotheses The data collected were analyzed using simple mean, standard deviation and t-test statistics, The findings showed that: (i) There is no significant difference in the test anxiety levels of the participants before exposure to treatments; (ii) test-wiseness training in Mathematics had positive impact on the adolescent secondary school students' test anxiety levels. Adolescent students without test-wiseness training in Mathematics are more test anxious than the adolescent students with test-wiseness training in mathematics. It is therefore recommended that test-wiseness training in Mathematics should be inculcated into the curriculum of both secondary schools and teacher training colleges. Teachers are also encouraged to add test-wiseness instruction to their regular Mathematics classes so that their students may become test-wise in a testing situation .