MEMS rate gyroscopes are prone to different errors because of environmental conditions and manufacturing errors. These errors can result to mismatch between the fabricated gyros and the designed ones. Different environmental conditions and disturbances can change the parameters and specifications of a gyro, and its sensitivity may deteriorate, since the parameters are different from the optimal ones. External linear acceleration is one of the main environmental disturbances that may change the behavior of an MEMS rate gyro that its effect on the accuracy of an MEMS proof mass gyroscope is found here. This is done by finding the equations of motion of gyroscope in presence of acceleration and solving the equations analytically and numerically and then surveying changes of calibration diagram of a typically designed gyro after addition of acceleration to the equations. Also, the error in angular velocity sensing will be found. It is seen that linear external acceleration can make a constant bias in the drive and sense mode responses in different angular velocities. But, change of sense mode amplitude in different external linear accelerations is very low. Angular velocity can be calibrated according to the sense mode amplitude or the maximum value of the output. The error percent of angular velocity measurement is very different in these two methods. © IMechE 2017.