In this work we propose a sequential test for the process capability index Cpmk. We study the statistical properties of the sequential test by performing an extensive simulation study with regard the average of the sample sizes for correctly deciding, for H0 and H1, the maximum allowable sample size required to achieve a pre-set power level and for ensuring that the empirical type I error probability does not exceed the nominal alfa-level of the test. We compared the performance of the sequential procedure with the properties of the most used non-sequential test. The results show that the proposed test allows on average smaller stopping sample sizes as compared with the fixed sample size test while maintaining the desired alfa-level and power.