Herein, we describe a new approach to make pools of microRNA targeting breast cancer cells. The microRNA pools were synthesized at once on the same solid support using the "Tandem Oligonucleotide Synthesis" strategy. We make up to four consecutive microRNAs (miR129-1-5p, miR31, miR206, and miR27b-3p) using 2'/3'OAc nucleotide phosphoramidites, with the total length of the pool reaching 88 nucleotides. The developed phosphoramidites, when combined, give a cleavable moiety that separates the microRNAs and is cleaved using standard post-RNA synthesis cleavage conditions. Furthermore, we investigate making branched pools (microRNA dendrimers) versus linear pools as a strategy to further improve the product yields. Our approach provides with microRNA pools in high yields, which is of relevance to the growing demand on synthetic RNA oligomers for nucleic acid research and technology.