The W51 star-forming cloud is one of the most active star-forming regions in the Milky Way. Using high-resolution (~200 au) ALMA data, we investigate the properties of protostellar cores in W51. The catalog of protostellar cores is extracted using the dendrogram source-identifying tool in both Band 3 and Band 6; we confirmed these sources by visual inspection. We measured the spectral indices of the cataloged objects from the flux comparison of two bands. The distribution of spectral indices is mostly at ~2, indicating that most of the objects are optically thick. We present the comparison of the properties of objects between our high-resolution data and the previous ALMA-IMF data with lower resolution (~2000 au) to understand how cores fragment and how the core mass function maps onto the stellar mass function. Our preliminary results show different fragmentation properties of W51E and W51 North, the two sub-regions of the W51 A cloud.