This paper investigates optimal content placement for wireless femto-caching network. The average bit error rate (BER) is formulated as a function of content placement under wireless fading. To minimize the average BER, we propose a greedy algorithm finding optimal content placement with low-computational complexity. Exploiting the property of the optimal content placement which we derive, the proposed algorithm can be performed over considerably reduced search space. Contrary to the optimal content placement without consideration of wireless fading aspects, we reveal that optimal content placement can be reached by balancing a tradeoff between two different gains: file diversity gain and channel diversity gain. Moreover, we also identify the conditions that the optimal placement can be found without running the proposed greedy algorithm and derive the corresponding optimal content placement in closed form.