A list of our research achievements on multiple aminoglycoside antibiotic (AG) resistance in AG-producing actinomycetes is outlined. In 1979, the author discovered a novel AG (istamycin)-producing Streptomyces tenjimariensis SS-939 by screening actinomycetes with kanamycin (KM)-resistance and plasmid profiles. This discovery directed our biochemical and genetic approaches to multiple AG resistance (AGR) of AG producers. In this article, the following discoveries will be outlined: 1. AGR profiles correlating with the productivity of AGs in AG-producers, 2. Wide distribution of multiple AG resistance in AG-nonproducing actinomycetes, 3. Involvement of ribosomal resistance and AG-acetylating enzymes as underlying AGR factors, 4. Activation by single nucleotide substitution of a silent gene coding for aminoglycoside 3-N-acetyltransferase, AAC(3), in S. griseus, 5. Discovery of a novel antibiotic indolizomycin through protoplast fusion treatment between S. tenjimariensis and S. griseus strains with different AGR phenotypes and 6. Double stage-acting activity of arbekacin (ABK; an anti-MRSA semisynthetic AG) discovered by acetylation of ABK with cloned AACs; i.e. both ABK and its acetylated derivatives showed remarkable antibiotic activities.