Sparse_dot_topn provides a fast way to performing a sparse matrix multiplication followed by top-n multiplication result selections. Comparing very large feature vectors and picking the best matches, in practice often results in performing sparse matrix multiplication followed by selecting the top-n multiplication results. In this package, we implement a customized Cython function for this purpose. When comparing our Cythonic approach to doing the same use with SciPy and NumPy functions, our approach improves the speed by about 40% and reduces memory consumption.