Harmful cyanobacterial blooms (HABs), primarily composed of toxic cyanobacteria like Microcystis aeruginosa, pose a significant threat to aquatic ecosystems and human health. Algicidal bacteria had emerged as a promising strategy for HAB control due to their safety and efficacy. In this study, the algicidal bacterium Streptomyces violaceorubidus lzh-14, isolated from Cha Lake in Dezhou, China, exhibited strong algicidal activity against M. aeruginosa. When bacterial culture was added to algal cultures at a final volume ratio of 10% (v/v), the algicidal activity reached 94.5% ± 1.8% after 72 h. Moreover, S. violaceorubidus lzh-14 showed varying degrees of algicidal activity against other tested cyanobacterial species. Microscopic observation revealed that M. aeruginosa cells treated with lzh-14 became deformed and ruptured, resulting in the leakage of cellular contents. The algicidal substance extracted from S. violaceorubidus lzh-14 demonstrated strong stability under varying temperatures and pH conditions. Based on these findings, algicidal powder was preliminarily developed. This study confirms that S. violaceorubidus lzh-14 and its active substance have potential as effective biocontrol agents against HABs.