<asp:Repeater ID="rptOuter" runat="server" DataSourceID="odsOuter"
        onitemdatabound="rptOuter_ItemDataBound">
        <ItemTemplate>
            <asp:Label ID="lblFirst" runat="server" Text='<%# Eval("first")%>'></asp:Label>
            <asp:Repeater ID="rptInner" runat="server" DataSourceID="odsInner">
                <ItemTemplate>
                    <asp:Label ID="lblSecond" runat="server" Text='<%# Eval("second")%>'></asp:Label>
                    <asp:Label ID="lblThird" runat="server" Text='<%# Eval("third")%>'></asp:Label>
                </ItemTemplate>
            </asp:Repeater>
        </ItemTemplate>
    </asp:Repeater>

protected void rptOuter_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    if ((e.Item.ItemType == ListItemType.Item) || (e.Item.ItemType == ListItemType.AlternatingItem))
    {
        ((Label)e.Item.FindControl("lblFirst")).Text = "New Text";

        ((Repeater)e.Item.FindControl("rptInner")).DataSource = "";
        ((Repeater)e.Item.FindControl("rptInner")).DataBind();//bind data to inner repeater..
    }
}