Heat transfer from an argon arc plasma jet at atmospheric pressure to a wall was investigated experimentally and theoretically. A new, water-cooled thermal probe was developed for measuring the plasma temperature and velocity. The temperature was determined from the measured heat flux by using an empirical relation for the heat transfer coefficient, taking into account the variable physical properties of the argon plasma. The measured temperature was in good agreement with those obtained from optical measurements. To clarify the effects of joule heating, re-combination of charged particles and electron working function on heat transfer to the wall, theoretical analysis near the stagnation point was performed and the results were compared with experimental data, where the local heat flux was measured by developing a new sensor. The results indicate that the most important heat transfer mechanism is heating by the electron work function.