en Infectious diseases and public health Infectious diseases and public health Original article Original article <strong>Introduction: </strong><em>Giardia lamblia</em> is a protozoan parasite with universal distribution in human populations. This infections transfer to human via contaminated foods and waters with <em>Giardia </em>cysts. The Knowledge on the incidence of this agent in the potential infection sources can provide valuable information for control and the spread of this parasite to human communities. This study was aimed to isolate and identify the <em>Giardia </em><em>lamblia</em> cysts in the surface waters of Rasht city, Guilan province, north of Iran with microscopy and PCR assay. <strong>Methods</strong>: This cross-sectional study was performed on 45 samples of surface waters collected from rivers and wetlands in the vicinity of Rasht city. The samples were concentrated using nitrocellulose membrane filters, and the sediments were examined for <em>Giardia </em>cysts by microscopy with a magnification of 1000 X. Also, DNA was extracted from the sediments, and the heat shock protein gene of <em>G. lamblia</em> was amplified. <strong>Results</strong>: From 45 samples, 33.33% and 40% were positive by microscopy and PCR, respectively. <strong>Conclusion:</strong> In comparison with the standard microscopic method, PCR showed more sensitivity for detection of <em>G. lamblia</em> cysts in water samples. Giardia lamblia Cysts, Surface Water, PCR, Rasht 8 12 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-144-2&slc_lang=en&sid=1 Elham saeedi esaeedi82@gmail.com 0000-0003-4164-3291 No Department of Biology, Rasht Branch, Islamic Azad University, Rasht, Iran Nematollah Jonaidi Jafari Jonaidii.2000@yahoo.com 0000-0002-6006-7771 No Health Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran Ali Salehzadeh salehzadehmb@yahoo.com 0000-0003-4238-0999 Yes Department of Biology, Rasht Branch, Islamic Azad University, Rasht, Iran