Background In Jordan, Diabetes Mellitus (DM) is the fifth leading cause of death. The important keystones in preventing DM complications are performing Self-Care Behaviors (SCB) such as diabetic Medication Adherence (MA) and engaging in Physical Activity (PA). The Theory of Planned Behavior (TPB) illustrates the relationship between three major constructs: behavioral attitudes, subjective norms (SN), and perceived behavioral control (PBC). The combination of the three constructs will shape the patient's behavior (i.e., performing SCB).The objectives of this study are to assess the diabetic MA and PA levels (i.e., adequate and inadequate) among Jordanian diabetic patients, assess the frequency of the levels of TPB constructs (i.e., behavioral attitudes, SN, and PBC) regarding diabetic MA and PA among Jordanian diabetic patients, identify the patients, identify the predictors of PA adherence among Jordanian diabetic patients, detect the relationships between participants' demographics and TPB constructs regarding SCB (MA and PA) among the participants, and detect the relationships between the TPB constructs among the participants. Methodology The current study uses a cross-sectional correlation design and convenience sampling to recruit 400 (Female = 144, Male = 156) diabetic patients from four public hospitals in Jordan as participants. Based on the TPB, two tools (MA & PA) are modified and used to collect the data regarding the factors that are associated with patients' diabetic MA and engagement in PA.The used tools include subscales consisting of items rated on a five-point. Likert scale constructed to measure the independent variables of attitude, SN, PBC, and demographic variables to perform the two SCBs. Results Around one quarter of the patients (n=112, 28%) had an HbA1clevel higher than 8; about half of the study participants (n= 219, 54.8%) had inadequate diabetic MA, and about two thirds of the sample (n=260, 65%) had inadequate adherence to PA. The findings of a regression model illustrated that four factors were significantly predictors to diabetic MA: marital status (p=0.03), DM complication type (p= 0.001), SN (p=0.001), and PBC (p=0.001). In relation to performing PA, the regression model indicated that the following factors were significant predictors: presence of DM complication (p=0.001), SN (p=0.01), and PBC (p= 0.001). Finally, three constructs of TPB correlated significantly with each other. Conclusion There are several chronic illnesses in Jordan nowadays; however, diabetes could be the most prevalent. This could lead to a higher burden on both the health care personnel (such as the physicians and the nurses) and the patients themselves. The health care providers should build their practices on the latest knowledge available in the diabetes field. Clinical instructors and nursing educators in nursing schools can utilize the results (demographic variables and TPB constructs) of the current study to educate patients about what to expect if they adhere to diabetic medications. The Electronic Health Record of the patients should reflect the predictors of both MA and PA adherence. Thus, nurses' assessment will be focused on the major factors that affect the patient's adherence. Publication of the study findings in highly prestigious nursing journals with high impact factors is highly recommended. Furthermore, the researcher could present the findings of the study at both local and international nursing conferences. Replication of this study using a larger and more diverse sample is highly recommended