Friction Stir Welding (FSW) is one method of solid state welding where welded joints are formed without the addition of filler metal. The pin shape design in the welding tool is a very important parameter in welding FSW. This research was conducted to know the influence of pin tool form on welding FSW dissimilar aluminum 1xxx series and 5xxx series aluminum. The welding process uses a variety of threaded cylindrical tool pin shapes, non-threaded cylinders, threaded and tapered cylinders with a tool rotating speed of 985 rpm and a feed rate of 5 mm / min. The material used in this study was 1xxx series aluminum plate and 5xxx series aluminum with a length of 100 mm, width of 60 mm and thickness of 5 mm. Furthermore, the results of the welded joint were tested for macro and microstructure, hardness and tensile test. The results of the macro structure testing showed that there were defects in the form of incomplate penetration on the welding results in all variations of the pin tool shape, while in the microstructure testing of the weld zone the deformation and heating during the FSW process made the grain dimensions and shapes smooth and tight compared to other area. In the area of HAZ 1xxx series aluminum and 5 xxxx series all the results of the weld was an elongated black line which was the interface area between 1xxx series aluminum raw material and 5xxx series aluminum. The results of the hardness test showed that the highest hardness value was found in the use of non-threaded tapered tool pin shape at 72.7 VHN, while the lowest hardness value was on the use of non-threaded cylindrical tool pin shape of 46 VHN. For the results of tensile testing the highest tensile strength values were found in welding using the form of non-threaded cylindrical tool pin with a value of 86.98 mpa or 79.65% of the raw material of 1xxx series aluminum and 48.98% of the 5xxx series aluminum raw material, while the lowest tensile strength value was found in welding using the form of non-threaded tapered tool pin of 59.57 mpa or 54.55% of raw material of 1xxx series aluminum and 33.54% of 5xxx series raw material