Reverberation chambers are cost-effective tools for evaluating Multiple-Input Multiple-Output (MIMO) Over-The-Air (OTA) communication devices performance in both indoor and outdoor urban channel models. Their performance is typically assessed by using several figures-of-merit (FOM), such as MIMO Capacity, which evaluates the amount of information that can be reliably transmitted over a communications channel. Nevertheless, scarce publications about the effect of the environment characteristics, such as delay spread, on this figure-of-merit can be found in the literature. In this contribution, we analyze the dependence of MIMO Capacity on channel delay spread, by means of a multi-antenna OTA communication system using a QPSK modulation. For that purpose, channel RMS delay spread has been varied inside the reverberation chamber loading it with different quantities of absorbing material.