The study was conducted to detect the effect of giardiasis on human disaccharidase levels. Forty patients attending the medical outpatient department of PGIMER, Chandigarh were enrolled. Twenty patients, positive for Giardia lamblia comprised the study group while 20 patients negative for Giardia lamblia were taken as controls. Upper gastrointestinal endoscopy was performed in all patients. Estimation of lactase, sucrase, maltase and trehalase was done in biopsies. Histopathological investigation was carried out in all biopsy specimens after Haematoxylin and Eosin staining. Complaints of pain abdomen and bloating occurred commonly in giardiasis. Four biopsy samples in study group showed mild increase in lymphomononuclear infiltrate. Giardia lamblia was detected in 7 biopsies. Lactase levels were decreased significantly (p < 0.05) in giardiasis. Rest of the enzymes were comparable to the controls. No differences in the enzyme activities were observed between males and females in either group and with the duration of symptoms.