ONIONIS ONE OF THE MOST PRODUCTS OF AGRONOMIC AND GARDEN THAT CULTIVATED IN MORE FROM ONE HUNDRED COUNTRY OF WORLD. ONION HAS EFFICIENCY THAN TO OTHER CROPS FOR PRODUCTION CROP AND IS RICH AS VITAMIN RESOURCE, NECESSARY AMINO ACID, OTHER COMPOSITION AND MEDICINAL ATTRIBUTE. SALINITY IS A MAJOR LIMITATION OF ENVIRONMENT FOR PRODUCTION OF AGRONOMICAL CROPS IN DRY AND SEMI-DRY ZONES. IN ORDER TO OBTAIN OF HIGH PRODUCTION AND RESISTANCE TO STRESS CONDITIONS, IT IS NECESSARY TO USE FROM MUTAGENIC METHOD. THIS STUDY DESIGNED IN ORDER TO STUDY OF CYTOGENETICALLY VARIATION OF FOUR POPULATIONS OF IRANIAN ONION IN TWO ENVIRONMENTS OF SALINITY AND NORMAL. THIS STUDY WAS CARRIED OUT BY HEMATOXYLIN METHOD. AFTER OBTAIN ACCURATE MEIOTIC LEVELS, KARYOTYPE CHARACTERS INCLUDE TOTAL LENGTH CHROMOSOME, ASYMMETRIC INDEX OF WITHIN AND BETWEEN CHROMOSOME, TOTAL FORM, ASYMMETRIC INDEX AND KARYOTYPE FORMULA MEASURED.ANALYSIS OF VARIANCE SHOWED SIGNIFICANT DIFFERENECES AMONG POPULATIONS, SALINITY AND THEIR INTERACTIONS(P³0.01).RESULTS ALSO SHOWED THAT STUDIED POPULATIONS ARE DIPLOID AND NUMBER OF BASE WAS X=8. ALL POPULATIOS LOCATED IN CLASS OF 2C ESTIBEANS SYMMETRIC EXCEPTION TO POPULATION OF GOM UNDER SALINITY ENVIRONMENT AND DORCHEH UNDER NORMAL CONDITION THAT INDICATED STUDIED POPULATIONS HAVE THE MOST EVOLUTIONARY. CLUSTER ANALYSIS ON THE BASIS ALL STUDIED CHARACTERS CLUSTERED POPULATIONS IN DIFFERENT FOUR GROUPS. ON THE BASIS, DORCHEH POPULATION LOCATED IN A GROUP AND KASHAN POPULATION LOCATED IN THE OTHER GROUP. RESULT SHOWED THAT SALINITY MAY CHANGE EVALUATION.