Spot welding is a method of joining metals by welding, on the surface of plates that are joined to each other at the same time an electric current is applied so that the surface becomes hot and melts due to electrical resistance. ST40 steel is a steel with a maximum tensile strength of 40 kg/mm², namely 40 steel is contained in low-carbon steel with a carbon content of 0.025% - 0.25% C. This study aims to determine the results of tensile strength testing in welded joints using spot welding on ST40 steel material. Quantitative research approach. The research technique used is experimental. The research location is at the Mechanical Engineering Laboratory of Ekasakti Padang University and the Integrated Laboratory of Padang State University. From the specimen with a time of 20 seconds, the average values were obtained: Maximum Tensile Stress [σu] [555.9 N/], Yield Stress [σy] [219.09 N/], Strain [ε] [0.11244%], Modulus of Elasticity(E)(494,397.01 N/). And the time of 25 seconds obtained the average value: Maximum Tensile Stress[σu] [441.995 N/], Yield Stress [σy] [188.57 N/], Strain [ε] [0.09538 %], Modulus of Elasticity [E] [463,404.27 N/]. And the time of 30 seconds obtained the average value: Maximum Tensile Stress(σu)(397.85 N/), Yield Stress(σy)(72.485 N/), Strain(ε)(0.05402 %), Modulus of Elasticity[E] [736.486.48 N/]. Based on the results of the study, it shows that the results of tensile strength based on the time of emphasis on spot welding are applied. The average value with 20 seconds welding press time has higher and greater tensile stress, yield stress, and strain than with 25 seconds and 30 seconds welding press time, It shows that the joint with 20 seconds welding press time is better and stronger compared to 25 seconds and 30 seconds welding press time.