When considering whether an employee is fairly dismissed or not, the court shall normally take both substantive fairness and procedural fairness into its account. However, there is a legal problem on whether an employerûs dismissal would still be considered legally fair if an accused employee is dismissed without passing through all disciplinary investigation procedures specified by the work rules or collective bargaining agreement prior to the dismissal. Regarding this, the Thai Supreme Court delivers its decisions into two distinct ways. The first one is that even though the disciplinary investigation procedures are not in line with work rules or collective bargaining agreement, the employerûs dismissal could still be considered fair if he could demonstrate that he has reasonable reason to dismiss such an employee.While the other one views that even though the employer has his reasonable reason to dismiss an employee, if all investigation procedures specified by work rules or collective bargaining agreement are not fully taken, such dismissal could be considered unfair. The author agrees with the later one as it takes both substantive fairness and procedural fairness into its account. However, due to contributory fault of both the employer and the employee, the court may determine an amount of damages for unfair dismissal to be less or even zero according to the circumstances and the gravity of the employeeûs fault.