One of the latest trends in modern welding industry is joining materials with different physical properties. Performing such welded joints results from the needs of the modern industry (like aviation or automotive). It is required that welded joints have appropriate strength, anti-corrosion and heat properties. The welded joints of this type are quite troublesome due to the large differences between the materials being joined. This work presents numerical and experimental research of laser butt welding of dissimilar materials. Experimental tests were made for laser welding of S355 steel with 304 austenitic steel (X5CrNi18-10). Macroscopic research is performed. On the basis of experimental research numerical investigations of the thermomechanical phenomena of the welding process are carried out using commercial software. Numerical analysis takes into account temperature dependent thermomechanical properties of welded materials. The temperature distribution in the welded joint is determined on the basis of results of calculations. The shape of melted zone and heat affected zone are numerically estimated. Stress distributions and displacement field in welded joint are numerically determined. Obtained results of the numerical analysis are compared to the experimental results.