A robust controller was developed for SUBARU22/100, 100kW variable speed pitch controlled wind turbine, using Mu-Synthesis. It provides more sophisticated robust controller than H-Infinity, as structured uncertainties are considered in the design model. Non-linear simulations showed its robustness in model errors as much as 200% of pitch delay, 500% of generator time constant, and 200% of speed sensor delay. The power curve measured in a field test was shown to be improved significantly than former PI controller. As smaller turbines are more difficult to be controlled than larger ones, present achievement is promising for large turbines. It contributes not only to performance improvement but also to structural damage reduction in turbulent conditions, to cost reduction, and to on-site tuning free.