We study about the Gaussian MIMO X channel and the Gaussian MIMO Z channel. In Gaussian MIMO X channel we have two multiple antennas in a transmitter and a receiver. One of the cross-links in the MIMO X channel is eliminated to obtain the MIMO Z channel. The sum-rate upper bound is derived for the MIMO Z channel and it is examined with an other existing bound. From the sum-rate upper bound of the MIMO Z channel we can obtain the sum-rate upper bound of the MIMO X channel. Again, the sum-rate upper bound of the MIMO X channel is obtained from the derived worst noise covariance matrix for two user multiple access channel. The sum-rate of MIMO X channel is further increased by reducing the detection of unknown signals using some detection algorithms. The derived sum-rate upper bounds for the MIMO X channel are compared with the Maddah Ali Motahari khandani (MMK) scheme. The above results are considered with MIMO interference channel and their results are examined. On further examining we derive some numerical values, which shows that the obtained sum-rate upper bounds capacity is much more tighter than the previous ones. © Research India Publications.