The purpose of this study was to calculate and compare the volume of hidden blood loss (HBL) and perioperative blood loss between open posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) by Wiltse approach.We retrospectively analyzed 143 patients between March 2017 and December 2017, they were randomly divided into PLIF group and TLIF group. The following information were collected on admission: patient’s age, gender, height, weight, body mass index (BMI), surgery levels, surgical time, duration time, disorder type, intraoperative bleeding, wound drainage, visual analog scale (VAS) scores, neurological complications, transfusion rate. Preoperative and postoperative hematocrit (Hct) were recorded in order to calculate total blood loss (TBL) according to Gross’s formula. To calculate each patient’s HBL, chi-square test and Student’s t test were used to analyze data.Patients in PLIF had a mean TBL of 1144 ± 356 mL, and the mean HBL was 486 ± 203 mL, 43.9 ± 16.2% of the TBL. While patients in TLIF, the mean TBL was 952 ± 303 mL, and the mean HBL was 421 ± 178 mL, 44.7 ± 17.0% of the TBL. Hence, there was significant difference in TBL and HBL between 2 groups, respectively (P = .000, P = .044). However, there was no difference in the ratio of the HBL between 2 groups (P = .797).The volume of HBL is lower in open TLIF by Wiltse approach than that in PLIF, which may be a large proportion of TBL in posterior lumbar fusion surgery. Comprehensive understanding of HBL can contribute to keep patient safety and better to rehabilitation in perioperative.