Multimorbidity, known as multiple chronic conditions (MCCs), is the co-existence of two or more chronic health conditions (CHC). The near-retirement-age population with MCC is more likely to experience discontinued labor force participation (LFP). Our objective was to evaluate the impact of MCC on LFP among adults aged 50-64 and to explore heterogeneous effects between self-employed and non-self-employed workers. We constructed our sample using the Health and Retirement Study (HRS) from 1996 to 2018. We adopted an individual fixed-effect (F.E.) model and Propensity Score Matching (PSM) to measure the impact of MCC on the probability of being employed and changes in annual work hours. 50.5% of respondents have MCC. Individuals with MCC exhibit a predicted probability of being employed that is 9.3 percentage points (P<0.01, 95% CI: -0.109, -0.078) lower than those without MCC. Compared with non-CHC, MCC significantly reduced annual working hours by 6.1% (P<0.01, 95% CI: -0.091, -0.036) in the F.E. model and by 4.9% (P<0.01, CI: -0.064, -0.033) in PSM estimation. The effect is more pronounced for the self-employed with MCC, who have 13.0% (P<0.05, CI: -0.233, -0.026) fewer annual work hours than non-CHCs based on the FE model and 13.4% (P<0.01, CI: -0.197, -0.070) in PSM estimation. MCC significantly reduces LFP compared with non-MCC. MCC has a heterogeneous impact across occupational types. It is important to support the near-retirement-age working population with multimorbidity through effective clinical interventions and workplace wellness policies to help manage health conditions and remain active in the labor market.