[Solved]-How to set all border widths except bottom border-Highcharts

You need to set lineWidth for xAxis, to overlap plotBorderWidth, see: http://jsfiddle.net/3Nczq/

$('#container').highcharts({
    chart: {
        type: 'line',
        plotBorderColor: 'red',
        plotBorderWidth: 2
    },
    title: {
        text: 'plotBorderWidth is set to one pixel'
    },
    xAxis: {
        lineWidth: 2,
        categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
    },

    series: [{
        data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]
    }]
});