Molecular hydrogen occurs in two forms, the so-called ortho-hydrogen and para-hydrogen. At a temperature of 293 K and above, hydrogen has 75% of ortho- and 25% para-content. The content of para-hydrogen increases with falling temperature. At a temperature of 20 K almost 100% para-hydrogen is present. While hydrogen is cooled down and liquefied the exothermic natural conversion starts, but much slower than the liquefaction itself. However, the conversion can be accelerated by using a catalyst. To avoid an unintentionally evaporation due to the exothermic ortho to para conversion it is important to verify that the conversion is completed before the liquid hydrogen is stored, transported or used. To accelerate and to ensure a complete conversion an oversized ortho/para-catalyst is normally used. However, the activity of the catalyst decreases over time. Therefore, a continuous in-situ measurement of the ortho/para-ratio can contribute to effective use of the catalyst and can help to reduce hydrogen losses due to unintentional evaporation. A measurement system based on Raman-spectroscopy is currently being developed at the ZEA-1. First tests with the measuring system show promising results on a laboratory scale. The aim of these investigations is to develop a compact measuring system that measures the ortho/para concentration of liquid hydrogen in-situ.