Background–Dengue and chikungunya fever are vector borne arboviral diseases that have been circulating globally in the various tropical and sub tropical regions. India being an endemic country for dengue and chikungunya, every or alternative year. Circulation of both the viruses along with presence of common mosquito vector (Aedes aegypti and albopictus) Aims and objectives: To study seroprevalance of dengue and chikungunya co–infection ,early diagnosis and their seasonal trends .Materials and methods–This was a prospective laboratory based study conducted at JLN Medical College and associated group of Hospitals, Ajmer from March 2018 to October 2019 . Clinically suspected patients of dengue and/or chikungunya from all the outpatient and inpatient departments were enrolled as cases.Serum samples were tested for the IgM antibodies of dengue and chikungunya both by ELISA method.Results–Out of 965 samples ,156(16.16%) found only dengue antibodies,88(9.11%) only chikungunya antibodies and 83(8.6%) both antibodies . If the co–infection concluded than the total number of dengue and chikungunya positive were 239(24.76%) and 171(17.72%) respectively . Majority of the patients belonged to the age group of 21–30 years, followed by 31–40 years with preponderance of males over females. Maximum number of patients were reported in post monsoon.Conclusion–As the clinical features of dengue and chikungunya virus infections are mostly similar, so it is advisable to test for both viruses . Fever and headache were the universal symptoms observed in Dengue, Chikungunya and co–infection . Present study shows that occurrence of dengue, chikungunya and their co–infection were more in post–monsoon season, middle age group and in males than females,so vector control ,personal protective measures and early diagnosis is very important to reduce mortality rate .