Cognitive radios are of interest because they are capable of high frequency utilization efficiency. In a cognitive radio, multiband receivers are required to make use of unused frequency bands. On the other hand, MIMO (multiple-input multiple-output) spatial multiplexing is also used to increase transmission capacity. This paper proposes a multiband MIMO receiver with ordered successive detection based on heterodyne reception. Because the use of an RF-BPF (radio frequency-bandpass filter) with a wide pass band is required in the receiver for multiband reception, the heterodyne receiver suffers from image-band interference. Therefore, the proposed receiver is designed not only to detect spatially multiplexed signals but also to suppress image-band interference. Computer simulation shows that the proposed receiver achieves superior BER performance even in the presence of strong image-band interference signals.