MicroRNAs belong to non-coding RNAs with regulatory significance and are ~22 nucleotides long. miRNAs are transcribed from various transcription units within the genome. Processing of primary microRNA transcripts is sequentially carried out within the nucleus and cytoplasm by RNase-ⅠⅠⅠ proteins Drosha, and Dicer respectively. Dicer processed mature miRNA duplex is eventually loaded onto AGO protein forming RISC effector complex. Following RISC loading, the miRNA duplex is unwound, guide strand selection, and passenger strand removal follows. Within the miRNA duplex, both of the strands are equally capable and any of the two can be preferred by RISC as guide strand, however, the strand which shows thermodynamic unstability at 5′ end is preferred as guide strand. miRNA biogenesis is regulated by various factors including certain RNA modifications that have been observed in the stem region of several pre-miRNAs. Moreover, RNA binding proteins regulate miRNAs post-transcriptionally. Rbfox family RNA binding proteins bind through their RRM domain to (U)GCAUG motifs. Rbfox-2 binds to Fox binding element in the terminal loop of pre-miR-20b and regulates its processing and strand bias, favoring 5p strand selection. In the absence of Rbfox-2 binding, miR-20b-5p cellular levels significantly lower, and miR-20b-3p levels are unaltered. This finding suggests a novel function of Rbfox proteins in determining the strand selection of miRNAs.