Mesoporous chromium-based terephthalate metal-organic framework (MIL-101) encapsulated Keggin phosphotungstic acid (HPW) [MIL-101(HPW)] was demonstrated to be an active heterogeneous catalyst for selective catalysis of the ring opening reaction of styrene oxide with methanol achieving 99 % yield of 2-methoxy-2-phenylethanol in 20 minutes at 40 °C. Similar MIL-101 samples prepared using one-pot microwave synthesis in the absence of HPW or in the presence of hydrofluoric acid (HF) were less active. The impact of fluoride and HPW polyanions incorporation on the acidity of MIL-101 was investigated by in situ Infrared spectroscopy technique using CO as a probe molecule. Additional hydroxyl groups and Lewis acid sites are present in MIL-101(HPW) explaining the observed superior catalytic performance in styrene oxide methanolysis.