Since the proliferation of software product in the (semi)automation of business operations, most especially software product developed using the object-oriented methodology; the quality of the design of software becomes significant. The measurement of the quality attributes of software during and after development guides software developers in ensuring the production of software products that are maintainable. Several metrics have been proposed for the measurement of the inheritance hierarchy of object-oriented software designs. This paper presents an empirical validation of two inheritance-based metrics: Average Understandability (AU) and Average Modifiability (AM), for the estimation of the modifiability of object-oriented software inheritance hierarchies. Data collected from two open-source object-oriented software are used for the empirical validation of the metrics. The results of the study show that the two metrics are good indicators of the modifiability of object-oriented inheritance hierarchy from high level designs perspective. © 2014 IEEE.