Objective <p>Internal fixation is the usual treatment for undisplaced intracapsular hip fractures (Garden I and II). This study aimed to determine the optimal rehabilitation protocol for patients undergoing femoral neck system (FNS) fixation.</p> Methods <p>A prospective randomized controlled trial (RCT) was conducted involving 58 patients who underwent FNS fixation for femoral neck fractures (FNFs) during a 10-month period from September 2023 to June 2024. They were randomly assigned to two groups: an immediate weight-bearing and early ambulation (IWBEA) group (within 48&#xa0;h) and a delayed weight-bearing and ambulation (DWBA) group (after 6&#xa0;weeks). Outcomes included time of hospitalization, fracture healing time, in-hospital complications, functional performance, pain severity, and activities of daily living.</p> Results <p>The IWBEA group showed a shorter time of hospitalization [median 6.0 (IQR 5.0–7.0) days vs. 7.0 (IQR 6.5–13.5)&#xa0;days, <i>P</i> = 0.002], a lesser fracture healing time [median 11.0 (IQR 10.0–12.5) weeks vs. 12.0 (IQR 11.0–13.0) weeks, <i>P</i> = 0.040], and a lower rate of in-hospital complications (6.9% vs. 27.6%, <i>P</i> = 0.037). At 12-month follow-up, activities of daily living [median 100.0 (IQR 95.0–100.0), <i>P</i> = 0.350], functional performance [median 12.0 (IQR 11.0–12.0), <i>P</i> = 0.289], pain severity [median 1.0 (IQR 0.0–2.0), <i>P</i> = 0.765], and Avascular Necrosis (AVN) incidence (<i>χ</i>² = 1.673, <i>P</i> = 0.196) were comparable between groups.</p> Conclusions <p>The IWBEA rehabilitation protocol can reduce time of hospitalization, fracture healing time, and incidence of in-hospital complications. In undisplaced intracapsular hip fractures treated with FNS, an IWBEA should be preferred.</p> Trial registration <p>Chinese Clinical Trial Registry (ChiCTR2500099199).</p>