For example, a wireless communication device may be configured to determine a Resource Unit (RU) allocation of a plurality of RUs to a plurality of wireless communication stations (STAs), respectively, the RU allocation to allocate to a STA of the plurality of STAs an RU of the plurality of RUs, wherein an RU size of the RU allocated to the STA is based at least on a traffic rate parameter, which is dependent on a traffic rate of Downlink (DL) traffic for the STA; and to transmit a Multi-User (MU) DL Orthogonal-Frequency-Division-Multiple-Access (OFDMA) Physical-layer Protocol Data Unit (PPDU) to the plurality of STAs according to the RU allocation.