There are different sources of allergenic glutathione transferase proteins (GST), including house dust mites and helminths. In the genus Ascaris, it is expected that GST family comprises at least 6 isoforms; but only information about allergenic properties of a sigma-like GST is available. However, a pi-class isoform was also identified in a purified native GST fraction from Ascaris, displaying differential IgE reactivity among tested patients (Acevedo et al, PloS one. 2013;8(11):e78353). Here, we characterize the allergenic activity of a recombinant pi-class GST isolated from Ascaris suum, its enzymatic properties and the relationship of its humoral response with infection burden. Pi-class GST (rGSTP) was produced as a recombinant product in BL21(DE3). Glutathione binding was evaluated with affinity agarose and its enzymatic activity using CDNB. Homology with other isoforms was analyzed with BLAST. rGSTP-specific IgE and IgG4 levels were assessed by ELISA in 173 subjects from an A. lumbricoides endemic rural area (infection rate: 66%) located in the North Coast of Colombia, and compared with data from ABA-1, a nematode-resistant marker. CD203c-based basophil activation test (BAT) was performed in 8 sensitized patients and 2 negative controls. Ascaris infection burden was quantified as eggs per gram of feces by Kato Katz method. The relationships among infection burden and antibody response to rGSTP and ABA-1 were evaluated by generalized linear models (GLM), including age and gender as potential confounders. rGSTP showed moderate identity/similarity with omega-GST (22%/42%) and Asc s 13 (22%/47%). As expected, rGSTP showed activity against CDNB and bound to glutathione agarose. Sensitization rate to rGSTP was 37.6%. About 12% (20/173) of subjects were mono-sensitized (no response to omega-GST or Asc s 13). IgG4 reactivity to rGSTP was 70.5%. Basophils from sensitized patients were not activated by rGSTP. By GLM, it was observed that rGSTP-specific IgE (β: 0,69 ±SE: 0,28; p=0,01) were positively associated with Ascaris egg counts. There was no association between rGSTP-specific IgG4 and egg counts (β: 0,67 ±SE: 0,69; p=0,33). In contrast, ABA-1 specific IgE was inversely associated to Ascaris egg counts (β: -2,73 ±SE: 1,36; p=0,04) and ABA-1 specific IgG4 showed a positive direction (β: 0,39 ±SE: 1,91; p=0,04). The pi-like GST of Ascaris suum is an IgE reactive isoform with confirmed enzymatic activity. The lack of basophil activation capacity suggests a low allergenic activity. The strength of IgE responses seems to be more related to Ascaris infection burden, but not to protective immunity.