<style name="YourAnimation.Activity" parent="@android:style/Animation.Activity">
       <item name="android:windowEnterAnimation">@anim/your_in_down</item>
       <item name="android:windowExitAnimation">@anim/your_out_down</item>
    </style>

<style name="YourTheme" parent="android:Theme.Translucent">
       ...
       <item name="android:windowAnimationStyle">@style/YourAnimation.Activity</item>
    </style>

<activity
        android:name=".YourActivity"
        android:theme="@style/YourTheme" />

<style name="YourTheme" parent="android:Theme.Translucent">
   ...
    <item name="android:windowAnimationStyle">@style/YourAnimation.Activity</item>
</style>

<style name="YourAnimation.Activity" parent="@android:style/Animation.Activity">
    <item name="android:activityOpenEnterAnimation">@anim/slide_in_right</item>
    <item name="android:activityOpenExitAnimation">@anim/slide_out_left</item>
    <item name="android:activityCloseEnterAnimation">@android:anim/slide_in_left</item>
    <item name="android:activityCloseExitAnimation">@android:anim/slide_out_right</item>
</style>