In deep sclerectomy, collagen implant has been used to maintain space under the scleral flap. However, the effect of other implants has not been studied. In this retrospective study, we compared surgical outcomes between small collagen and chromic catgut used as implants in deep sclerectomy. Deep sclerectomy was performed on 23 patients (25 eyes) who either had an open angle and a high intraocular pressure (IOP) (> 22 mmHg) in spite of receiving the maximal tolerable medical treatment, or who were intolerant to medications. Our study consisted of 14 patients (15 eyes) in the small collagen group and 8 (9 eyes) in the chromic catgut group. The mean follow-up period was 8.6 ± 3.3 months in the small collagen group and 4.4 ± 1.2 months in the chromic catgut group. The mean preoperative IOP was not significantly different between the two groups. The complete success rate of the small collagen group was significantly better than that of the chromic catgut group at the final follow-up when data were analyzed using the Kaplan-Meier survival curve (87% versus 30%; P = .01). As for the qualified success rate, the small collagen group showed significantly better results at the final follow-up (93% versus 80%; P = .046). The mean number of postoperative medications was significantly lower in the small collagen group (0.26 versus 1.10; P < .05). These results confirmed that the use of small collagen implant in deep sclerectomy produced a higher success rate and a lowered need for postoperative medication compared to the use of chromic catgut implant. Because equal sized implants were used, the difference in biochemical properties, particularly the severity of inflammation caused by the implant, is presumed to be the cause of the different surgical outcomes.