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Glycogen and poly-3-hydroxybutyrate (PHB) are excellent biopolymer products from cyanobacteria. In this study, we demonstrate that nitrogen metabolism is positively influenced by the exogenous application of trehalose (Tre) in <i>Arthrospira platensis</i> under nitrogen-deprived (−N) conditions. Cells were cultivated photoautotrophically for 5 days under −N conditions, with or without the addition of exogenous Tre. The results revealed that biomass and chlorophyll-<i>a</i> content of <i>A. platensis</i> experienced enhancement with the addition of 0.003 M and 0.03 M Tre in the −N medium after one day, indicating relief from growth inhibition caused by nitrogen deprivation. The highest glycogen content (54.09 ± 1.6% (<i>w</i>/<i>w</i>) DW) was observed in cells grown for 2 days under the −N + 0.003 M Tre condition (<i>p</i> < 0.05), while the highest PHB content (15.2 ± 0.2% (<i>w</i>/<i>w</i>) DW) was observed in cells grown for 3 days under the −N + 0.03 M Tre condition (<i>p</i> < 0.05). The RT-PCR analysis showed a significant increase in <i>glgA</i> and <i>phaC</i> transcript levels, representing approximately 1.2- and 1.3-fold increases, respectively, in <i>A. platensis</i> grown under −N + 0.003 M Tre and −N + 0.03 M Tre conditions. This was accompanied by the induction of enzyme activities, including glycogen synthase and PHA synthase with maximal values of 89.15 and 0.68 µmol min⁻¹ mg⁻¹ protein, respectively. The chemical structure identification of glycogen and PHB from <i>A. platensis</i> was confirmed by FTIR and NMR analysis. This research represents the first study examining the performance of trehalose in promoting glycogen and PHB production in cyanobacteria under nitrogen-deprived conditions.