In this paper, we propose a radio resource allocation (RRA) scheme for multiuser multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) systems in order to achieve the optimal system throughput. The proposed RRA algorithm adaptively schedules 3-dimension (3-D) (space, frequency and time) slots to different users according to various channel state information (CSI). Different from most of conventional RRA algorithms, the proposed algorithm joins scheduling process with power allocation, that is, iteratively allocating total transmit power into resource block (RB) during 3-D slot assignment. The power allocation is an extension of the space-frequency waterfilling algorithm, and is adapted to an equivalent 1-D single input single output (SISO) channels. The equivalent SISO channels are obtained from the original 3-D RBs in the sense of the same maximum achievable throughput. The proposed algorithm was confirmed in the World-wide interoperability for Microwave Access (WiMAX) systems following IEEE 802.16e media access control (MAC) protocols. It is shown that the proposed RRA algorithm significantly simplifies the scheduling process and achieves more throughput than round robin (RR) scheme.