Introduction: Occupational Health and Safety (OHS) for formal sector workers is held along with regulations, joint commitments, training, and continuous monitoring. This condition cannot be applied for informal sector, so it approaches that can be performed such as activating social support from workers’ environment. This study aimed to determine for social support to improve the knowledge, attitude and practice of OHS workers in informal sector. Methods: This study a quasi-experimental with pre-posttest and control group design. Subjects were 90 limestone workers taken by Multistage Sampling from Gunungkidul Regency, Indonesia. Subjects were divided into health promotion by family support and peer support (FS&PS), peer support (PS), family support (FS), and control (C) group with treatment period of one month. Variables were measured using a knowledge, attitude, and practice questionnaire. The obtained data then analyzed using Kruskal-Wallis test and Mann-Whitney test. Results: There was a significant difference (p<0.001) in the knowledge, attitude and practice of OHS in limestone workers. FS&PS group gave the highest score for knowledge variable. There was no significant differences between OHS attitude between FS&PS and FS only (p=0.787). The biggest influence of attitude changes was from the FS group. The OHS practice has no significant differences between PS and C group (p=0.696), while other groups have significant differences. Conclusion: The biggest influence of changes in OHS practice was in the FS group. The combination of FS&PS is more effective in increasing knowledge, while attitude and practice are more effective if involving FS.