Climatic changes in Rokan Hulu Regency lead to the occurrence of floods, droughts, high rainfall. These phenomena caused changes in cropping patterns and disruption of agricultural production. The shift of seasons and changing rainfall patterns resulted in delayed harvesting. In addition, prolong dry seasons caused by geothermal heat may cause fires resulting in loss of harvest. The effects of Ethylene on four varieties of chilies planted in the Rokan Hulu Regency on the growth and yield of chili were determined. The study comprised two factors, the first was that five levels of ethylene were utilised, 0 ppm which was the control, and four concentrations of ethylene namely 100 ppm, 200 ppm, 300 ppm and 400 ppm. The second factor was the four varieties of chilies used, three of the varieties were elite hybrids commercially available while the fourth was a local variety commonly found in Rokan Hulu. The parameters recorded included plant height, leaf width, leaf length and increasing number of productive branches of chili. It was observed that for all the parameters measured variety 4, the local variety gave the best results when treated with 400ppm ethylene. This study is expected to be used as guidelines chili cultivation in Rokan Hulu Regency. [ABSTRACT FROM AUTHOR]