The operation of mineral processing units or plants is related to the mineral composition of the ore. However, unit performances are usually characterized in terms of metal content or recovery as this data is easier to be obtained rather than the mineral content. This paper presents a data reconciliation method that combines material balancing calculations and mineral stoichiometric information to estimate balanced mineral composition, chemical assays and flow rates in various streams of a mineral processing plant. The advantage of this method is evaluated by comparing the variance of the reconciled variables from this method to those obtained from usual data reconciliation methods. The estimated mineral composition leads to improved process performance evaluation.