Peptide and protein drugs are currently under rapid development attributed to their high potency and efficacy in therapy.Their delivery, however, is limited by the short half-life,rapid degradation and clearance.Here, we present a high content phospholipids-based phase separation gel (PPSG) which is readily injectable and rapidly transform into an in situ implant gel after injection upon exposure to an aqueous environment.A selected peptide, octreotide acetate, achieved sustained release profiles for one month in rats.In addition, the local irritation caused by ethanol contained in PPSG can be eliminated by partially replacing ethanol with medium chain triglyceride.The mechanisms underlying phase transition and non-irritation of PPSG are based on water-insolubility of phospholipid and reduced ethanol diffusion.Our findings demonstrate that PPSG is a readily injectable, highly safe and efficient in situ forming implant for sustained delivery of peptides or proteins.