How to set bold title in Action Bar?

Can you please try with this:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <style name="MyTheme" parent="@android:style/Theme.Holo.Light">
    <item name="android:actionBarStyle">@style/MyTheme.MyActionBar</item>
  </style>

  <style name="MyTheme.MyActionBar"parent="@android:style/Widget.Holo.Light.ActionBar">
    <item name="android:titleTextStyle">@style/MyTheme.MyActionBar.TitleTextStyle</item>
  </style>

  <style name="MyTheme.MyActionBar.TitleTextStyle" parent="@android:style/TextAppearance.Holo.Widget.ActionBar.Title">
    <item name="android:background">#81CFEB</item>
    <item name="android:textStyle">bold</item>
  </style>
</resources>

For those using AppCompat, you'll need something like this:

<style name="MyTheme" parent="Theme.AppCompat">
    <item name="android:actionBarStyle">@style/MyTheme.ActionBar</item>
    <item name="actionBarStyle">@style/MyTheme.ActionBar</item>
</style>

<style name="MyTheme.ActionBar" parent="Widget.AppCompat.ActionBar.Solid">
    <item name="titleTextStyle">@style/MyTheme.ActionBar.TitleTextStyle</item>
</style>

<style name="MyTheme.ActionBar.TitleTextStyle" parent="TextAppearance.AppCompat">
    <item name="android:background">#81CFEB</item>
    <item name="android:textStyle">bold</item>
</style>