Whisker growth in Pb-free solder joints is one of the most reliability concerns in electronic industry. Several theories and models were developed to elaborate whisker growth, and many attempts were made to find solutions to solve this issue. Micro alloying, such as introducing Cu, Bi, Ag etc. into solders, is considered to be one of effective method to mitigate whisker growth. However, when alloying with these metal elements, the structure of solders will be changed, therefore the reliability of solders needs to be reevaluated. The purpose of this research is to explore the possibility to mitigate whisker growth by reinforce strategy without destroying the structure of solders. In this study, a novel reinforcement, nano-structured cage-type polyhedral oligomeric silsesquioxane (POSS), was employed and expected to mitigate whisker growth. POSS was added into Sn, Sn3.0Ag0.5Cu and Sn58Bi solders respectively. Whisker growth behaviors of these modified solders under high humidity and temperature environment (85 ℃, 85% relative humidity) were analyzed and discussed. The results indicated that, the driving force of whisker growth was compressive stress generated by the volume expanding of tin oxides. The high humidity and temperature condition facilitated the formation of tin oxides and therefore provided continuous driving force for whisker growth. POSS addition could inhibit oxidation process of metal tin effectively, and reduce the amount of tin oxides formation, consequently whisker growth was mitigated. Among Sn, Sn3.0Ag0.5Cu and Sn58Bi solders, Sn solders was the easiest one to grow whiskers, while Sn58Bi was at the lowest risk to grow whis-kers.