If you are talking about Hibiscus rosa-sinensis, that symptom usually means that it is getting too much water, or too little water too often. Sometimes, in containers, it can mean that it is getting too stressed between soakings, and you may have to water more often--ask yourself if it is wilting between soakings. If so, water a little more often. If no, water a little less often, allowing the top cm of soil to dry before watering again. In the ground, Hibiscus likes deep soaking, wetting the top 1/2 meter of soil, then going dry for a week or two before watering again, depending on the temperature.
Hope this helps!