When the rejection region is taken on both ends of the sampling distribution, the test is called two-sided test or two-tailed test. When we are using a two-sided test, half of the rejection region equal to  is taken on the right side and the other half equal to  is taken on the left side of the sampling distribution. Suppose the sampling distribution of the statistic is a normal distribution and we have to test the hypothesis  against the alternative hypothesis  which is two – sided. is rejected when the calculated value of  is greater than  or it is less than . Thus the critical region is  or, it can also be written as .
When is rejected, then  is accepted. Two-sided test is shown in the figure.