Small nuclear RNAs (snRNAs) are vital for eukaryotic cell activities and play important roles in pre-mRNA splicing. The molecular mechanism underlying the transcription of snRNA, regulated via upstream/downstream cis-elements and relevant trans-elements, has been investigated in detail using cell-free extracts. However, the processing of precursor snRNA (pre-snRNA), which is required by 3' end maturation of pre-snRNA, remains unclear as a proper processing assay is difficult to develop in vitro. Here, we present an in vitro method using synthetic labeled RNA as substrates to study the 3' cleavage of pre-snRNA.