Purpose: To study the relationship of the 1st to 2nd intermetatarsal angle(1-2 IMA) between the intra-operative and weight bearing postoperative anterior-posterior(AP) radiography, and evaluate the intra-operative predictability for the postoperative 1-2 IMA after proximal metatarsal osteotomy(PMO) in the hallux valgus deformity. Materials and Methods: 20 cases of moderate to severe hallux valgus patients were included in this study. After the oblique PMO(Ludloff procedure) was performed and the osteotomy site was fixed temporarily, the AP view was taken intra-operatively. About 10 weeks after surgery, postoperative weight bearing AP view was taken. The pre -. intra -, and postoperative 1-2 IMAs were compared and ana lysed statistically. Results: The 1-2 IMAs of the weight bearing preoperative, non-weight bearing intra-operative and weight bearing postoperative AP view were $15.9^{circ}{pm}1.8^{circ},;4.7^{circ}{pm}2.1^{circ}$, and $6.8^{circ}{pm}2.5^{circ}$ (Mean${pm}$SD) respectively. The postoperative 1-2 IMA was greater than intra-operative measurement by $2.1^{circ}{pm}1.8^{circ}$ (range; $-1^{circ}$ to $6^{circ}$) which was stastistically significant(p<0.05). To get less than $9^{circ}$ postoperatively as an average normal, intra-operative 1-2 IMA should be within $3.8^{circ}$ to $5.2^{circ}$ (95% confidence interval), and intra-operative 1-2 IMA should be within $3.4^{circ}{pm}$to $5.4^{circ}$(95% confidence interval) to get more than $6^{circ}$ difference between preoperative and postoperative 1-2 IMA, which is regarded as more than average correction by the distal metatarsal osteotomy. Conclusion: In hallux valgus surgery, it should be considered that intra-operative 1-2 IMA was less than the postoperative. To achieve postoperative 1-2 IMA less than $9^{circ}$ and more than correction angle of $6^{circ}$, it is suggested that the intra-operative 1-2 IMA should be measured less than about $5^{circ}$.