Hi ahmadsubuhanl...,

Set titleTextStyle in the option.

Check this example. Now please take its reference and correct your code.

HTML

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript" src="https://www.google.com/jsapi"></script>
<script type="text/javascript">
    google.load("visualization", "1", { packages: ["corechart"] });
    google.setOnLoadCallback(drawChart);
    function drawChart() {
        var options = {
            title: 'USA City Distribution',
            titleTextStyle: {
                color: "red",               // color 'red' or '#cc00cc'
                fontName: "Courier New",    // 'Times New Roman'
                fontSize: 25,               // 12, 18
                bold: true,                 // true or false
                italic: true                // true of false
            },
            width: 600,
            height: 400,
            bar: { groupWidth: "95%" },
            legend: { position: "none" },
            isStacked: true
        };
        $.ajax({
            type: "POST",
            url: "Default.aspx/GetChartData",
            data: '{}',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (r) {
                var data = google.visualization.arrayToDataTable(r.d);
                var chart = new google.visualization.BarChart($("#chart")[0]);
                chart.draw(data, options);
            },
            failure: function (r) {
                alert(r.d);
            },
            error: function (r) {
                alert(r.d);
            }
        });
    }
</script>
<div id="chart" style="width: 900px; height: 500px;">
</div>

Code same as article.

Create Dynamic Google Bar Chart in ASP.Net using C# and VB.Net

Screenshot