Purpose - The purpose of this paper is to introduce a modified $MC_p$ by considering the effect of gauge measurement error on the multivariate process capability index. Design/methodology/approach - In this paper, the effect of measurement system on the quality characteristics appears as coefficient matrix A which changes the variance-covariance matrix of quality characteristics ${sum}$, into A ${sum}$. In this case, the authors investigate the properties of multivariate index and present adjusted confidence intervals and critical values for capability testing purpose of this index. Findings - The results show that the simplicity of the obtained index, calculating the true process capability by using empirical process capability and also computing the critical value and power of the process capability testing is simpler in this modified approach. Originality/value - The results presented in this paper would help practitioners to determine their actual process capability and see if their processes meet the preset capability requirement, and then make reliable decisions.