藻青素（英语cyanophycin），即多聚-L-精氨酰-聚(L-天冬氨酸)，是一种非蛋白质，不在核糖体合成的氨基酸多聚物，包括由天冬氨酸组成的骨架和精氨酸的侧链基团。

藻青素最早于1887年由意大利科学家Borzi检测到，发现于多数蓝藻和少数异养细菌中，如不动杆菌属(Acinetobacter)等中。藻青素在生理条件下基本不可溶，并在缺乏磷或硫时在细胞质内积累形成颗粒，总体来说在生长曲线的早稳定期或中稳定期。藻青素用作氮（或者有碳）的保存物质，同时作为蓝藻异形胞固氮时的氮缓冲剂。氮和碳可由胞内的藻青素酶（英文cyanophycinase）动员成为天冬氨酸-精氨酸二肽的形式。

Cyanophycin, or multi-L-arginyl-poly (L-aspartic acid), is a non-protein, non-ribosomally produced amino acid polymer composed of an aspartic acid backbone and arginine side groups.

Cyanophycin was first detected in 1887 by the Italian botanist Antonino Borzì and can be found in most cyanobacteria and a few heterotrophic bacteria such as Acinetobacter sp. Cyanophycin is largely insoluble under physiological conditions and is accumulated in the form of granules in the cytoplasm during phosphate or sulfur starvation, generally in the early and mid-stationary phase. It is used as a nitrogen- and possibly carbon-storage compound and also serves as a dynamic buffer for fixed nitrogen in cyanobacterial heterocysts. Nitrogen and carbon are mobilized from cyanophycin by intracellular cyanophycinase in the form of aspartate-arginine dipeptides.