Plant Growth Promoting Rhizobacteria (PGPR) are commonly used to produce biofertilizers. As such, the purpose of the present research was to develop a PGPR biofertilizer formulation from four Streptomyces strains isolated from millipede fecal pellets and to select suitable carriers for them. The four Streptomyces isolates were Streptomyces sp. KLS-AC04, S. zaomyceticus KLD-AC02-1, S. zaomyceticus KLD-AC16 and S. zaomyceticus KLD-AC30. Their compatibility was tested on Actinomycetes isolation agar by the cross-streak method and the results showed that the four isolates can coexist. A viability test was done with three different types of carriers: coconut coir, cow dung and peat moss. The best carrier for all isolates was peat moss (viability: 5.3 x 104 − 8.5 x 105 cfu/g). The isolate that exhibited the highest survival rate across the three carriers was Streptomyces sp. KLS-AC04. Seven PGPR biofertilizer formulations were developed, of which formulation 6 (cow dung: peat moss: KLS-AC04: KLD-AC02-1: KLD-AC16: KLD-AC30) showed the highest viability (6 x 105 cfu/g). The effects of the PGPR biofertilizer formulations on plant growth were explored on Chinese kale. This showed that the use of the four Streptomyces strains had a significant positive effect on germination percentage (range 47.5% − 80.0%), fresh weight (range 0.060 − 0.086 g), shoot length (range 36.1 − 60.4 mm), and root length (range 15.3 − 30.8 mm).