This　paper　presents　a　mobile　robot　guidance　approach　based　on　tracking　of　straight　line　marked　on　the　ground.　To　accurately　and　robustly　extract　the　ground　line,　a　senior　line　detector,　with　sub-pixel　centre　localization　of　capability　for　a　stripe　like　narrow　region,　is　successfully　presented.　PD　and　PID　are　designed　for　mobile　robot　tracking　control　and　their　performances　are　compared　in　experiment.　From　the　experimental　results,　the　effectiveness　and　usefulness　of　the　proposed　guidance　system　are　confirmed.