Microalgae　are　considered　as　excellent　candidates　for　bioactive　compounds,　yet　microalgal　residues　remaining　after　the　extraction　of　one　or　two　compounds　are　usually　discarded,　which　is　not　economical.　This　study　demonstrates　the　alkaline　extraction　of　proteins　from　Chlorella　pyrenoidosa　residue　after　lipid　and　pigment　extractions,　and　their　functional　properties.　Single-factor　experiments　and　response　surface　methodology　were　used　to　obtain　the　optimal　conditions　for　protein　extraction.　Based　on　our　results,　a　maximum　protein　yield　of　722.70　mg/g,　was　obtained　under　the　following　extraction　conditions:　sodium　hydroxide　concentration　7.90%,　extraction　temperature　70.00　degrees　C,　extraction　time　34.80　min,　and　microalgal　residue　concentration　8.20　mg/mL.　The　molecular　weight　of　microalgal　residue　protein　isolate　(MRPI)　was　mainly　distributed　at　the　regions　of　0.18-0.50　kDa,　0.50-1.50　kDa,　and　1.50-5.00　kDa.　The　essential　amino　acid　content　was　greater　than　the　values　recommended　by　FAO/WHO　standards;　a　high　essential　amino　acid　index　value　(1.49)　was　another　good　indication　that　MRPI　is　suitable　for　human　consumption.　Moreover,　MRPI　exhibited　excellent　emulsifying　properties　and　antioxidant　activity,　which　suggests　it　may　be　useful　as　an　emulsifying　agent　and　antioxidant.　These　findings　could　improve　the　extraction　methods　of　functional　protein　from　microalgal　residue　and　add　value　to　microalgae-based　bioactive　compound　production　processes.