A carbon steel(A53) in this study is used as material of pipe in marine plant and ship industry. An weld to connect carbon steels is necessary and an effect of weld on properties of carbon steel has been completed by many researchers. In this study, dynamic behavior of welded carbon steel is studied by acoustic emission(AE) technique, one of nondestructive tests. There are lots of AE parameters to analyze the damage behavior of carbon steel by external loading. AE parameters of energy, cumulative count, amplitude and AE event were used, and each parameter was differentiated according to the damage degree of carbon steel. Energy showed high level at elastic range of load curve, while amplitude was the highest value at the hardening region. Cumulative count showed similar growth tendency with loading curve. In addition, ultrasonic technique and hardness test were applied to evaluate the mechanical properties according to the base zone, HAZ region and weld zone of the weld specimen. The velocity and attenuation ratio showed a little of change according to the each zones, and the evaluation of ultrasonic wave on the each zone of the specimen was an useful method to clarify the mechanical properties of the carbon steel.