With advances in chemotherapy, conversion surgery is often performed for initially unresectable colorectal cancer liver metastasis (CLM). However, unexpected posthepatectomy liver failure (PHLF) is sometimes associated with chemotherapy-associated liver injuries following long-term chemotherapy. We aimed to identify predictive factors for PHLF after conversion surgery for initially unresectable CLM. We retrospectively identified 774 consecutive patients who underwent initial liver resections for histologically confirmed CLMs between 2010 and 2019 at our institute. We enrolled 107 patients with initially unresectable CLMs. Clinicopathological characteristics were evaluated to determine their association with PHLF. Logistic regression analysis was performed to analyze the predictors of PHLF. Among the 107 patients, PHLF occurred in 15 cases (14%). Multivariate analysis revealed that splenomegaly during preoperative chemotherapy (> 135%) was an independent risk factor for PHLF (P = 0.002; odds ratio 14.30; 95% confidence interval 2.69-76.08). In the analysis limited to the splenomegaly group, lower platelet counts, increased blood loss and operative times, and large liver resection areas (> 100 cm2) were significant risk factors for PHLF (P = 0.018, 0.043, 0.020, and 0.024, respectively). Among them, a liver resection area > 100 cm2 can be calculated preoperatively and correlate with a complex hepatectomy. These findings could help predict PHLF after conversion surgery and induction chemotherapy for initially unresectable CLMs. Careful decisions, including detailed procedures and timing of hepatectomy, should be made before conversion hepatectomy in patients who develop splenomegaly after induction chemotherapy and require complex hepatectomies with a large liver resection area.