Deep object detectors suffer from the gradient contribution imbalance during training. In this paper, we point out that such imbalance can be ascribed to the imbalance in example attributes, e.g., difficulty and shape variation degree. We further propose example attribute based prediction modulation (EAPM) to address it. In EAPM, first, the attribute of an example is defined by the prediction and the corresponding ground truth. Then, a modulating factor w.r.t the example attribute is introduced to modulate the prediction error. Finally, the new prediction and the ground-truth are input into the loss function. Essentially, we adjust the gradients of examples with specific attributes to reweight their contribution on the global gradients. We apply EAPM with focal loss and balanced L1 loss to simultaneously solve the imbalance in classification and localization. The experimental results on MS COCO demonstrate that EAPM can bring substantial improvement for deep object detectors.