We performed longitudinal plasma proteomics analysis and determined absolute protein levels in a Canadian cohort (n=74) at admission day to hospital for acute COVID-19 and at 3 and 6 months after diagnosis of acute COVID-19. We measured plasma protein on a triple quadrupole mass spectrometer operated in multiple reaction monitoring mode and used internal standards to deduce protein absolute concentrations. We used a validated panel of 269 surrogate heavy labeled peptides. We also measured % predicted forced vital capacity (FVC, %) and diffusing capacity of the lungs for carbon monoxide (DLCO, %) by routine pulmonary function testing. We did functional enrichment and pathway analyses and determined proteins that were increased or decreased from hospital admission to 3-months and 6-months, compared females to males and determined associations of proteins with FVC% and DLCO%.